(svn r25055) [1.3] -Backport from trunk:

- Fix: Refactor Script Debug GUI to only set widget states in OnInvalidateData [FS#5490] (r25052)
- Fix: Do not let gcc include files from the "standard C" include directories; newer gcc/libc seem to otherwise automatically include some header files at the top of the preprocessed nfo files which causes NFOrenum/GRFcodec to make invalid assumptions about the NFO version (r25050)
- Fix: Minimise gaps feature caused removal to only happen at the signal build interval instead of the implicit interval of 1 [FS#5479] (r25038)
- Fix: Green path signals would be shown when building them 'under' a train, and they would keep showing green until they were passed again [FS#5480] (r25037)

config.lib

@@ -3648,6 +3648,9 @@ showhelp() {
 	echo "  LDFLAGS                        linker flags, e.g. -L<lib dir> if you"
 	echo "                                 have libraries in a nonstandard"
 	echo "                                 directory <lib dir>"
+	echo "  CFLAGS_BUILD                   C compiler flags for build time tool generation"
+	echo "  CXXFLAGS_BUILD                 C++ compiler flags for build time tool generation"
+	echo "  LDFLAGS_BUILD                  linker flags for build time tool generation"
 	echo ""
 	echo "Use these variables to override the choices made by 'configure' or to help"
 	echo "it to find libraries and programs with nonstandard names/locations."