Allow overriding CC on macos & freebsd.

Other platforms allow overriding CC in the bootstrap build by setting CC
in the environment, but macos & freebsd were setting it back to clang.
Similarly, if CONFIG_CC is set in the tup.config, the actual tup build
for macos & freebsd would ignore that value and just use clang.

Now the CC environment variable for bootstrapping and CONFIG_CC for the
tup build should work for setting the compiler in all cases.

Fixes #497.

Tuprules.tup

@@ -6,17 +6,6 @@ else
 TARGET = @(TUP_PLATFORM)
 endif
 
-ifdef CC
-CC = @(CC)
-else
-ifeq ($(TARGET),win32)
-CC = x86_64-w64-mingw32-gcc
-CC32 = i686-w64-mingw32-gcc
-else
-CC = gcc
-endif
-endif
-
 ifeq (@(TUP_DEBUG),y)
 CFLAGS += -Og
 else
@@ -88,11 +77,24 @@ endif
 !dot = |> ^ DOT %f^ dot -Efontname="Vernada, serif" -Nfontname="Vernada, serif" -Efontsize=10 -Nfontsize=10 -Tpng %f > %o |>
 !cp = |> ^ CP %f -> %o^ cp %f %o |>
 
+# Default to using gcc to compile. This is overridden on some OSes in the
+# included $(TARGET).tup file, and can be overridden by the user in the
+# tup.config file by setting CONFIG_CC (and/or CONFIG_CC32 on Windows).
+CC = gcc
+
 TUP_MONITOR = null
 TUP_SUID_GROUP = root
 TUP_USE_SYSTEM_PCRE = y
 include $(TARGET).tup
 
+ifdef CC
+CC = @(CC)
+endif
+
+ifdef CC32
+CC32 = @(CC32)
+endif
+
 ifdef TUP_USE_SYSTEM_PCRE
 use_system_pcre = @(TUP_USE_SYSTEM_PCRE)
 else

build.sh

@@ -30,7 +30,7 @@ else
 	exit 1
 fi
 LDFLAGS="$LDFLAGS -lm"
-: ${CC:=gcc}
+default_cc=gcc
 case "$os" in
 	Linux)
 	plat_files="$plat_files ../src/compat/dummy.c"
@@ -47,20 +47,21 @@ case "$os" in
 	plat_files="$plat_files ../src/compat/dummy.c"
 	plat_files="$plat_files ../src/compat/clearenv.c "
 	plat_cflags="$plat_cflags -include ../src/compat/macosx.h"
-	CC=clang
+	default_cc=clang
 	;;
 	FreeBSD)
 	plat_files="$plat_files ../src/compat/dummy.c"
 	plat_files="$plat_files ../src/compat/utimensat_linux.c"
 	plat_files="$plat_files ../src/compat/clearenv.c"
-	CC=clang
+	default_cc=clang
 	;;
 	NetBSD)
 	plat_files="$plat_files ../src/compat/dummy.c"
 	plat_files="$plat_files ../src/compat/clearenv.c"
 	plat_cflags="$plat_cflags -include ../src/compat/netbsd.h"
 	;;
 esac
+: ${CC:=$default_cc}
 
 rm -rf build
 echo "  mkdir build"

win32.tup

@@ -1,6 +1,5 @@
-ifdef CC32
-CC32 = @(CC32)
-endif
+CC = x86_64-w64-mingw32-gcc
+CC32 = i686-w64-mingw32-gcc
 
 # Compatibility function prototypes and include path for wrapper functions
 CFLAGS += -include $(TUP_CWD)/src/compat/win32/mingw.h