Append -g -Os rather than overwriting

Sync with GCC
	2014-11-17  Bob Dunlop  <bob.dunlop@xyzzy.org.uk>

	* mt-ospace (CFLAGS_FOR_TARGET): Append -g -Os rather than
	overwriting.
	(CXXFLAGS_FOR_TARGET): Similarly.

config/ChangeLog

@@ -1,3 +1,12 @@
+2015-03-16  H.J. Lu  <hongjiu.lu@intel.com>
+
+	Sync with GCC
+	2014-11-17  Bob Dunlop  <bob.dunlop@xyzzy.org.uk>
+
+	* mt-ospace (CFLAGS_FOR_TARGET): Append -g -Os rather than
+	overwriting.
+	(CXXFLAGS_FOR_TARGET): Similarly.
+
 2015-03-16  H.J. Lu  <hongjiu.lu@intel.com>
 
 	Sync with GCC

config/mt-ospace

@@ -1,3 +1,3 @@
 # Build libraries optimizing for space, not speed.
- CFLAGS_FOR_TARGET = -g -Os
- CXXFLAGS_FOR_TARGET = -g -Os
+ CFLAGS_FOR_TARGET += -g -Os
+ CXXFLAGS_FOR_TARGET += -g -Os