Merge branch 'maint-0.2.7' into maint-0.2.8

changes/bug18841.1

+  o Major bugfixes (compilation):
+    - Correctly detect compiler flags on systems where _FORTIFY_SOURCE
+      is predefined. Previously, our use of -D_FORTIFY_SOURCE would
+      cause a compiler warning, thereby making other checks fail.
+      Fixes one case of bug 18841; bugfix on 0.2.3.17-beta. Patch from
+      "trudokal".
+

configure.ac

@@ -761,7 +761,7 @@ AC_COMPILE_IFELSE([AC_LANG_PROGRAM([], [
 #endif])], have_clang=yes, have_clang=no)
 
 if test "x$enable_gcc_hardening" != "xno"; then
-    CFLAGS="$CFLAGS -D_FORTIFY_SOURCE=2"
+    CFLAGS="$CFLAGS -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=2"
     if test "x$have_clang" = "xyes"; then
         TOR_CHECK_CFLAGS(-Qunused-arguments)
     fi