objtool: Fix HOSTCC flag usage

HOSTCC is always wanted when building objtool. Setting CC to HOSTCC
happens after tools/scripts/Makefile.include is included, meaning
flags (like CFLAGS) are set assuming say CC is gcc, but then it can be
later set to HOSTCC which may be clang. tools/scripts/Makefile.include
is needed for host set up and common macros in objtool's
Makefile. Rather than override the CC variable to HOSTCC, just pass CC
as HOSTCC to the sub-makes of Makefile.build, the libsubcmd builds and
also to the linkage step.

Signed-off-by: Ian Rogers <irogers@google.com>
Link: https://lore.kernel.org/r/20230126190606.40739-4-irogers@google.com
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

Author: captain5050

tools/objtool/Makefile

@@ -2,11 +2,6 @@
 include ../scripts/Makefile.include
 include ../scripts/Makefile.arch
 
-# always use the host compiler
-AR	 = $(HOSTAR)
-CC	 = $(HOSTCC)
-LD	 = $(HOSTLD)
-
 ifeq ($(srctree),)
 srctree := $(patsubst %/,%,$(dir $(CURDIR)))
 srctree := $(patsubst %/,%,$(dir $(srctree)))
@@ -34,13 +29,18 @@ INCLUDES := -I$(srctree)/tools/include \
 	    -I$(srctree)/tools/objtool/include \
 	    -I$(srctree)/tools/objtool/arch/$(SRCARCH)/include \
 	    -I$(LIBSUBCMD_OUTPUT)/include
+# Note, EXTRA_WARNINGS here was determined for CC and not HOSTCC, it
+# is passed here to match a legacy behavior.
 WARNINGS := $(EXTRA_WARNINGS) -Wno-switch-default -Wno-switch-enum -Wno-packed -Wno-nested-externs
-CFLAGS   := -Werror $(WARNINGS) $(KBUILD_HOSTCFLAGS) -g $(INCLUDES) $(LIBELF_FLAGS)
-LDFLAGS  += $(LIBELF_LIBS) $(LIBSUBCMD) $(KBUILD_HOSTLDFLAGS)
+OBJTOOL_CFLAGS := -Werror $(WARNINGS) $(KBUILD_HOSTCFLAGS) -g $(INCLUDES) $(LIBELF_FLAGS)
+OBJTOOL_LDFLAGS := $(LIBELF_LIBS) $(LIBSUBCMD) $(KBUILD_HOSTLDFLAGS)
 
 # Allow old libelf to be used:
-elfshdr := $(shell echo '$(pound)include <libelf.h>' | $(CC) $(CFLAGS) -x c -E - | grep elf_getshdr)
-CFLAGS += $(if $(elfshdr),,-DLIBELF_USE_DEPRECATED)
+elfshdr := $(shell echo '$(pound)include <libelf.h>' | $(HOSTCC) $(OBJTOOL_CFLAGS) -x c -E - | grep elf_getshdr)
+OBJTOOL_CFLAGS += $(if $(elfshdr),,-DLIBELF_USE_DEPRECATED)
+
+# Always want host compilation.
+HOST_OVERRIDES := CC="$(HOSTCC)" LD="$(HOSTLD)" AR="$(HOSTAR)"
 
 AWK = awk
 MKDIR = mkdir
@@ -61,12 +61,14 @@ export BUILD_ORC
 export srctree OUTPUT CFLAGS SRCARCH AWK
 include $(srctree)/tools/build/Makefile.include
 
-$(OBJTOOL_IN): fixdep FORCE
+$(OBJTOOL_IN): fixdep $(LIBSUBCMD) FORCE
 	$(Q)$(CONFIG_SHELL) ./sync-check.sh
-	$(Q)$(MAKE) $(build)=objtool
+	$(Q)$(MAKE) $(build)=objtool $(HOST_OVERRIDES) CFLAGS="$(OBJTOOL_CFLAGS)" \
+		LDFLAGS="$(OBJTOOL_LDFLAGS)"
+
 
 $(OBJTOOL): $(LIBSUBCMD) $(OBJTOOL_IN)
-	$(QUIET_LINK)$(CC) $(OBJTOOL_IN) $(LDFLAGS) -o $@
+	$(QUIET_LINK)$(HOSTCC) $(OBJTOOL_IN) $(OBJTOOL_LDFLAGS) -o $@
 
 
 $(LIBSUBCMD_OUTPUT):
@@ -75,6 +77,7 @@ $(LIBSUBCMD_OUTPUT):
 $(LIBSUBCMD): fixdep $(LIBSUBCMD_OUTPUT) FORCE
 	$(Q)$(MAKE) -C $(LIBSUBCMD_DIR) O=$(LIBSUBCMD_OUTPUT) \
 		DESTDIR=$(LIBSUBCMD_OUTPUT) prefix= subdir= \
+		$(HOST_OVERRIDES) EXTRA_CFLAGS="$(OBJTOOL_CFLAGS)" \
 		$@ install_headers
 
 $(LIBSUBCMD)-clean: