Build libcgo.so with $(CC), not the gcc on PATH.

Change make.bash to make sure that $(CC) is defined to match
the compiler used to build the tools.

R=rsc
CC=golang-dev
https://golang.org/cl/1853041

src/libcgo/Makefile

@@ -26,13 +26,13 @@ LDFLAGS_freebsd=-pthread -shared -lm
 LDFLAGS_windows=-shared -lm -mthreads
 
 %.o: %.c
-	gcc $(CFLAGS_$(GOARCH)) -O2 -fPIC -o $@ -c $*.c
+	$(CC) $(CFLAGS_$(GOARCH)) -O2 -fPIC -o $@ -c $*.c
 
 %.o: %.S
-	gcc $(CFLAGS_$(GOARCH)) -O2 -fPIC -o $@ -c $*.S
+	$(CC) $(CFLAGS_$(GOARCH)) -O2 -fPIC -o $@ -c $*.S
 
 libcgo.so: $(OFILES)
-	gcc $(CFLAGS_$(GOARCH)) -o libcgo.so $(OFILES) $(LDFLAGS_$(GOOS))
+	$(CC) $(CFLAGS_$(GOARCH)) -o libcgo.so $(OFILES) $(LDFLAGS_$(GOOS))
 
 $(QUOTED_GOROOT)/pkg/$(GOOS)_$(GOARCH)/libcgo.so: libcgo.so
 	cp libcgo.so $(QUOTED_GOROOT)/pkg/$(GOOS)_$(GOARCH)

src/make.bash

@@ -12,6 +12,7 @@ unset CDPATH	# in case user has it set
 
 rm -f "$GOBIN"/quietgcc
 CC=${CC:-gcc}
+export CC
 sed -e "s|@CC@|$CC|" < "$GOROOT"/src/quietgcc.bash > "$GOBIN"/quietgcc
 chmod +x "$GOBIN"/quietgcc