Bug 1723245 - Disable --gc-sections when building with sanitizer coverage. r=firefox-build-system-reviewers,mhentges

Differential Revision: https://phabricator.services.mozilla.com/D122952

build/autoconf/compiler-opts.m4

@@ -109,7 +109,14 @@ dnl ========================================================
 dnl = Automatically remove dead symbols
 dnl ========================================================
 
-if test "$GNU_CC" -a "$GCC_USE_GNU_LD" -a -z "$DEVELOPER_OPTIONS" -a -z "$MOZ_PROFILE_GENERATE"; then
+SANCOV=
+case "$LIBFUZZER_FLAGS" in
+*-fsanitize-coverage*|*-fsanitize=fuzzer*)
+    SANCOV=1
+    ;;
+esac
+
+if test "$GNU_CC" -a "$GCC_USE_GNU_LD" -a -z "$DEVELOPER_OPTIONS" -a -z "$MOZ_PROFILE_GENERATE" -a -z "$SANCOV"; then
     if test -n "$MOZ_DEBUG_FLAGS"; then
         dnl See bug 670659
         AC_CACHE_CHECK([whether removing dead symbols breaks debugging],