Keep sed from mangling our CFLAGS
especially -frecord-gcc-flags, which was half removed because it contains -g

--- a/m4/subs.m4
+++ b/m4/subs.m4
@@ -80,13 +80,13 @@
 			debug_flags="-D_DEBUG -g -O0"
 			BIGOBJ_FLAGS=""
 			($CC --version | grep -q mingw) && BIGOBJ_FLAGS="-Wa,-mbig-obj"
-			CXXFLAGS="`echo $CXXFLAGS | sed s:-O.::` $debug_flags -fno-inline $BIGOBJ_FLAGS"
-			CFLAGS="`echo $CFLAGS | sed s:-O.::` $debug_flags"
+			CXXFLAGS="${CXXFLAGS} $debug_flags -fno-inline $BIGOBJ_FLAGS"
+			CFLAGS="${CFLAGS} $debug_flags"
 		;;
 		no|*)
 			debug_flags="-DNDEBUG"
-			CXXFLAGS="`echo $CXXFLAGS | sed 's:-g[[a-z-]]*\s::g' | sed 's:-g[[a-z-]]*$::'` $debug_flags"
-			CFLAGS="`echo $CFLAGS | sed 's:-g[[a-z-]]*\s::g' | sed 's:-g[[a-z-]]*$::'` $debug_flags"
+			CXXFLAGS="${CXXFLAGS} $debug_flags"
+			CFLAGS="${CFLAGS} $debug_flags"
 		;;
 	esac