Set TARGET_LIBGCC to -lgcc instead of full libgcc.a path

Because
1. "$(TARGET_CC) -print-libgcc-file-name" doesn't get specialized
   libgcc.a, although with proper flags like "-march=armv7-a" and
   "-mthumb" it does.
2. When TARGET_CC is clang and -gcc-toolchain points to correct
   GCC 4.6 directory, "$(TARGET_CC) -print-libgcc-file-name"
   prints only libgcc.a w/o path (ie. a bug in clang)

This bug didn't reveal because TARGET-get-linker-objects-and-libraries
was called too early before TARGET_LIBGCC is set

Change-Id: I5e49abdcf23aaa69cb5bf35f771164646b13849b
diff --git a/build/core/default-build-commands.mk b/build/core/default-build-commands.mk
index 79e2c6b..d31bc60 100644
--- a/build/core/default-build-commands.mk
+++ b/build/core/default-build-commands.mk
@@ -93,7 +93,7 @@
 # when applied to static libraries or object files.
 cmd-strip = $(PRIVATE_STRIP) --strip-unneeded $(call host-path,$1)
 
-TARGET_LIBGCC = $(shell $(TARGET_CC) -print-libgcc-file-name)
+TARGET_LIBGCC = -lgcc
 TARGET_LDLIBS := -lc -lm
 
 #