Merge branch 'sccache-opt' into 'master'

Add CC_WRAPPER support

See merge request redox-os/relibc!666

Makefile

@@ -6,6 +6,7 @@ CARGO?=cargo
 CARGO_TEST?=$(CARGO)
 CARGO_COMMON_FLAGS=-Z build-std=core,alloc,compiler_builtins
 CARGOFLAGS?=$(CARGO_COMMON_FLAGS)
+CC_WRAPPER?=
 RUSTCFLAGS?=
 export OBJCOPY?=objcopy
 
@@ -268,5 +269,5 @@ $(BUILD)/openlibm: openlibm
 	touch $@
 
 $(BUILD)/openlibm/libopenlibm.a: $(BUILD)/openlibm $(BUILD)/release/librelibc.a
-	$(MAKE) AR=$(AR) CC=$(CC) LD=$(LD) CPPFLAGS="$(CPPFLAGS) -fno-stack-protector -I$(shell pwd)/include -I$(TARGET_HEADERS)" -C $< libopenlibm.a
+	$(MAKE) AR=$(AR) CC="$(CC_WRAPPER) $(CC)" LD=$(LD) CPPFLAGS="$(CPPFLAGS) -fno-stack-protector -I$(shell pwd)/include -I$(TARGET_HEADERS)" -C $< libopenlibm.a
 	./renamesyms.sh "$@" "$(BUILD)/release/deps/"