Merge pull request #212 from inverse-inc/conditional_compiler_flags

Do not force -frecord-gcc-switches flag

general.make

@@ -1,3 +1,16 @@
+# Macros that allow testing for GCC flag existence
+try-run = $(shell set -e;                      \
+	TMP="/tmp/SOGo-gcc-flags-check.$$$$.tmp";  \
+	TMPO="/tmp/SOGo-gcc-flags-check.$$$$.o";   \
+	if ($(1)) >/dev/null 2>&1;                 \
+	then echo "$(2)";                          \
+	else echo "$(3)";                          \
+	fi;                                        \
+	rm -f "$$TMP" "$$TMPO")
+
+cc-option = $(call try-run,\
+	$(CC) $(1) -c -x c /dev/null -o "$$TMP",$(1),$(2))
+
 # Use GCC level 2 optimization by default
 # Might be overridden below
 ADDITIONAL_OBJCFLAGS=-O2
@@ -12,5 +25,5 @@ endif
 # information plus the compiler flags used; that can
 # be afterwards read with:
 # readelf -p .GCC.command.line /path/to/elf_file
-ADDITIONAL_OBJCFLAGS += -g -frecord-gcc-switches
+ADDITIONAL_OBJCFLAGS += -g $(call cc-option,-frecord-gcc-switches)