Add the compiler name, version and libs used to compile

This changes the behaviour of `tor --version` in such a way.
```console
src/app/tor --version
Tor version 0.4.5.1-alpha-dev (git-46ccde66).
Tor is running on Linux with Libevent 2.1.12-stable, OpenSSL 1.1.1h, Zlib 1.2.11, Liblzma 5.2.4, Libzstd 1.4.5 and Glibc 2.31 as libc.
Tor compiled with GCC version 10.2.0
```

Fixes #32102

changes/ticket32102

+  o Minor features (build informations):
+    - Add build informations to `tor --version` in order to ease reproducible
+      builds

configure.ac

@@ -9,6 +9,8 @@ AC_CONFIG_SRCDIR([src/app/main/tor_main.c])
 AC_CONFIG_MACRO_DIR([m4])
 
 configure_flags="$*"
+AC_DEFINE_UNQUOTED([CONFIG_FLAGS], ["$configure_flags"], [Flags passed to configure])
+
 
 # DO NOT EDIT THIS DEFINITION BY HAND UNLESS YOU KNOW WHAT YOU'RE DOING.
 #
@@ -421,6 +423,17 @@ AC_PROG_MAKE_SET
 AC_PROG_RANLIB
 AC_PROG_SED
 
+AX_COMPILER_VERSION
+AX_COMPILER_VENDOR
+
+AC_DEFINE_UNQUOTED([COMPILER_VERSION],["$ax_cv_c_compiler_version"], [Compiler version])
+AC_DEFINE_UNQUOTED([COMPILER_VENDOR],["$ax_cv_c_compiler_vendor"], [Compiler vendor])
+
+AS_CASE($ax_cv_c_compiler_vendor,
+        [gnu], AC_DEFINE([COMPILER],["GCC"],[Compiler name]),
+        AC_DEFINE([COMPILER],[],[Compiler name])
+)
+
 AC_ARG_VAR([PERL], [path to Perl binary])
 AC_CHECK_PROGS([PERL], [perl])
 AM_CONDITIONAL(USE_PERL, [test "x$ac_cv_prog_PERL" != "x"])

m4/ax_compiler_vendor.m4

+# ===========================================================================
+#    https://www.gnu.org/software/autoconf-archive/ax_compiler_vendor.html
+# ===========================================================================
+#
+# SYNOPSIS
+#
+#   AX_COMPILER_VENDOR
+#
+# DESCRIPTION
+#
+#   Determine the vendor of the C/C++ compiler, e.g., gnu, intel, ibm, sun,
+#   hp, borland, comeau, dec, cray, kai, lcc, metrowerks, sgi, microsoft,
+#   watcom, etc. The vendor is returned in the cache variable
+#   $ax_cv_c_compiler_vendor for C and $ax_cv_cxx_compiler_vendor for C++.
+#
+# LICENSE
+#
+#   Copyright (c) 2008 Steven G. Johnson <stevenj@alum.mit.edu>
+#   Copyright (c) 2008 Matteo Frigo
+#
+#   This program is free software: you can redistribute it and/or modify it
+#   under the terms of the GNU General Public License as published by the
+#   Free Software Foundation, either version 3 of the License, or (at your
+#   option) any later version.
+#
+#   This program is distributed in the hope that it will be useful, but
+#   WITHOUT ANY WARRANTY; without even the implied warranty of
+#   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
+#   Public License for more details.
+#
+#   You should have received a copy of the GNU General Public License along
+#   with this program. If not, see <https://www.gnu.org/licenses/>.
+#
+#   As a special exception, the respective Autoconf Macro's copyright owner
+#   gives unlimited permission to copy, distribute and modify the configure
+#   scripts that are the output of Autoconf when processing the Macro. You
+#   need not follow the terms of the GNU General Public License when using
+#   or distributing such scripts, even though portions of the text of the
+#   Macro appear in them. The GNU General Public License (GPL) does govern
+#   all other use of the material that constitutes the Autoconf Macro.
+#
+#   This special exception to the GPL applies to versions of the Autoconf
+#   Macro released by the Autoconf Archive. When you make and distribute a
+#   modified version of the Autoconf Macro, you may extend this special
+#   exception to the GPL to apply to your modified version as well.
+
+#serial 17
+
+AC_DEFUN([AX_COMPILER_VENDOR],
+[AC_CACHE_CHECK([for _AC_LANG compiler vendor], ax_cv_[]_AC_LANG_ABBREV[]_compiler_vendor,
+  dnl Please add if possible support to ax_compiler_version.m4
+  [# note: don't check for gcc first since some other compilers define __GNUC__
+  vendors="intel:     __ICC,__ECC,__INTEL_COMPILER
+           ibm:       __xlc__,__xlC__,__IBMC__,__IBMCPP__
+           pathscale: __PATHCC__,__PATHSCALE__
+           clang:     __clang__
+           cray:      _CRAYC
+           fujitsu:   __FUJITSU
+           sdcc:      SDCC, __SDCC
+           gnu:       __GNUC__
+           sun:       __SUNPRO_C,__SUNPRO_CC
+           hp:        __HP_cc,__HP_aCC
+           dec:       __DECC,__DECCXX,__DECC_VER,__DECCXX_VER
+           borland:   __BORLANDC__,__CODEGEARC__,__TURBOC__
+           comeau:    __COMO__
+           kai:       __KCC
+           lcc:       __LCC__
+           sgi:       __sgi,sgi
+           microsoft: _MSC_VER
+           metrowerks: __MWERKS__
+           watcom:    __WATCOMC__
+           portland:  __PGI
+	   tcc:       __TINYC__
+           unknown:   UNKNOWN"
+  for ventest in $vendors; do
+    case $ventest in
+      *:) vendor=$ventest; continue ;;
+      *)  vencpp="defined("`echo $ventest | sed 's/,/) || defined(/g'`")" ;;
+    esac
+    AC_COMPILE_IFELSE([AC_LANG_PROGRAM(,[
+      #if !($vencpp)
+        thisisanerror;
+      #endif
+    ])], [break])
+  done
+  ax_cv_[]_AC_LANG_ABBREV[]_compiler_vendor=`echo $vendor | cut -d: -f1`
+ ])
+])

src/app/config/config.c

@@ -4485,6 +4485,25 @@ options_init_from_torrc(int argc, char **argv)
 
   if (config_line_find(cmdline_only_options, "--version")) {
     printf("Tor version %s.\n",get_version());
+    printf("Tor is running on %s with Libevent %s, "
+            "%s %s, Zlib %s, Liblzma %s, Libzstd %s and %s %s as libc.\n",
+            get_uname(),
+            tor_libevent_get_version_str(),
+            crypto_get_library_name(),
+            crypto_get_library_version_string(),
+            tor_compress_supports_method(ZLIB_METHOD) ?
+            tor_compress_version_str(ZLIB_METHOD) : "N/A",
+            tor_compress_supports_method(LZMA_METHOD) ?
+            tor_compress_version_str(LZMA_METHOD) : "N/A",
+            tor_compress_supports_method(ZSTD_METHOD) ?
+            tor_compress_version_str(ZSTD_METHOD) : "N/A",
+            tor_libc_get_name() ?
+            tor_libc_get_name() : "Unknown",
+            tor_libc_get_version_str());
+    printf("Tor compiled with %s version %s\n",
+            strcmp(COMPILER_VENDOR, "gnu") == 0?
+            COMPILER:COMPILER_VENDOR, COMPILER_VERSION);
+
     return 1;
   }