Fix cross compiling on OS X.

- The OS X specific flags must not be set when cross compiling. Check for a
  MinGW compiler on OS X before adding them.
- Do not set CC explicitly in chinachippatcher, it will be set from Rockbox
  Utility's Makefile.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@31527 a1c6a512-1295-4272-9138-f99709370657

rbutil/chinachippatcher/Makefile

@@ -7,7 +7,6 @@
 # $Id$
 #
 CFLAGS = -g -Wall
-CC = gcc
 
 OUTPUT = chinachippatcher
 

rbutil/libtools.make

@@ -45,12 +45,14 @@ endif
 NATIVECC = gcc
 CC ?= gcc
 ifeq ($(findstring Darwin,$(shell uname)),Darwin)
+ifneq ($(findstring mingw,$(CROSS)$(CC)),mingw)
 # building against SDK 10.4 is not compatible with gcc-4.2 (default on newer Xcode)
 # might need adjustment for older Xcode.
 CC ?= gcc-4.0
 CFLAGS += -isysroot /Developer/SDKs/MacOSX10.4u.sdk -mmacosx-version-min=10.4
 NATIVECC ?= gcc-4.0
 endif
+endif
 WINDRES = windres
 
 BUILD_DIR ?= $(TARGET_DIR)build