Given the following objective-c file (call it example.m):

#import <Foundation/Foundation.h>

int main( int argc, const char *argv[] ) {
    NSLog (@"Hello world!");
    return 0;
}

Compiling with clang works fine:
clang -arch armv7 -fmodules -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS8.1.sdk  example.m -c -o example.o

Adding ccache fails:
ccache clang -arch armv7 -fmodules -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS8.1.sdk  example.m -c -o example.o

While building module 'Foundation' imported from example.m:1:
While building module 'CoreFoundation' imported from /System/Library/Frameworks/Foundation.framework/Headers/Foundation.h:6:
While building module 'Darwin' imported from /System/Library/Frameworks/CoreFoundation.framework/Headers/CoreFoundation.h:11:
In file included from <module-includes>:1:
/usr/include/sys/cdefs.h:680:2: error: Unsupported architecture
#error Unsupported architecture
 ^
While building module 'Foundation' imported from example.m:1:
While building module 'CoreFoundation' imported from /System/Library/Frameworks/Foundation.framework/Headers/Foundation.h:6:
While building module 'Darwin' imported from /System/Library/Frameworks/CoreFoundation.framework/Headers/CoreFoundation.h:11:
In file included from <module-includes>:3:
In file included from /usr/include/ctype.h:70:
In file included from /usr/include/runetype.h:42:
In file included from /usr/include/_types.h:27:
In file included from /usr/include/sys/_types.h:33:
/usr/include/machine/_types.h:34:2: error: architecture not supported
#error architecture not supported
 ^

Removing the "-fmodules" flag and compiling with ccache works:
ccache clang -arch armv7 -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS8.1.sdk  example.m -c -o example.o