stm32/Makefile: Quote libgcc path so spaces are not an issue.
Fixes
@@ -124,7 +124,7 @@ endif
LDFLAGS = -nostdlib -L $(LD_DIR) $(addprefix -T,$(LD_FILES)) -Map=$(@:.elf=.map) --cref
LDFLAGS += --defsym=_estack_reserve=8
-LIBS = $(shell $(CC) $(CFLAGS) -print-libgcc-file-name)
+LIBS = "$(shell $(CC) $(CFLAGS) -print-libgcc-file-name)"
# Remove uncalled code from the final image.
CFLAGS += -fdata-sections -ffunction-sections
