Add support for gcc compiler/linker hardening flags.

This patch adds support for two new configure options:
    '--enable-gcc-hardening'
    This sets CFLAGS to include:
        "-D_FORTIFY_SOURCE=2 -fstack-protector-all"
        "-fwrapv -fPIE -Wstack-protector -Wformat -Wformat-security"
        "-Wpointer-sign"
    It sets LDFLAGS to include:
        "-pie"

    '--enable-linker-hardening'
    This sets LDFLAGS to include:
        " -z relro -z now"

changes/compileTimeHardening

+Add two new configure flags:
+    --enable-gcc-hardening
+        This turns on gcc compile time hardening options. It ensures that
+        signed ints have defined behavior (-fwrapv), -D_FORTIFY_SOURCE=2 is
+        enabled (requiring -O2), stack smashing protection with canaries
+        (-fstack-protector-all), ASLR protection if supported by the kernel
+        (-fPIE, -pie). Additional security related warnings are enabled.
+        Verified as working on Mac OS X and Debian Lenny.
+
+    --enable-linker-hardening
+        This turns on ELF specific hardening features (relro, now). This does
+        not work with Mac OS X or any other non-ELF binary format.

configure.in

@@ -90,6 +90,27 @@ AC_ARG_ENABLE(gcc-warnings,
 AC_ARG_ENABLE(gcc-warnings-advisory,
      AS_HELP_STRING(--enable-gcc-warnings-advisory, [enable verbose warnings, excluding -Werror]))
 
+dnl Adam shostack suggests the following for Windows:
+dnl -D_FORTIFY_SOURCE=2 -fstack-protector-all
+dnl Others suggest '/gs /safeseh /nxcompat /dynamicbase' for non-gcc on Windows
+dnl This requires that we use gcc and that we add -O2 to the CFLAGS.
+AC_ARG_ENABLE(gcc-hardening,
+     AS_HELP_STRING(--enable-gcc-hardening, enable compiler security checks),
+[if test x$enableval = xyes; then
+    CFLAGS="$CFLAGS -D_FORTIFY_SOURCE=2 -fstack-protector-all"
+    CFLAGS+=" -fwrapv -fPIE -Wstack-protector -Wformat -Wformat-security"
+    CFLAGS+=" -Wpointer-sign"
+    LDFLAGS+=" -pie"
+fi])
+
+dnl Linker hardening options
+dnl Currently these options are ELF specific - you can't use this with MacOSX
+AC_ARG_ENABLE(linker-hardening,
+        AS_HELP_STRING(--enable-linker-hardening, enable linker security fixups),
+[if test x$enableval = xyes; then
+    LDFLAGS+=" -z relro -z now"
+fi])
+
 AC_ARG_ENABLE(local-appdata,
    AS_HELP_STRING(--enable-local-appdata, default to host local application data paths on Windows))
 if test "$enable_local_appdata" = "yes"; then