Update compiler workarounds for Clang 6.0

[Alexander Scherbatiy]

  Hi,

  I got the following message during building the JDK 9 on Mac OS X 
10.10 Yosemity:
------------
Compiling 32 properties into resource bundles
/Users/alexsch/openjdk/jdk9-modules/hotspot/make/bsd/makefiles/gcc.make:329: 
*** "Update compiler workarounds for Clang 6.0".  Stop.
------------

The installed gcc is:
---------------------
 > gcc --version
Configured with: --prefix=/Library/Developer/CommandLineTools/usr 
--with-gxx-include-dir=/usr/include/c++/4.2.1
Apple LLVM version 6.0 (clang-600.0.38) (based on LLVM 3.5svn)
Target: x86_64-apple-darwin14.0.0
Thread model: posix
---------------------

I also needs to remove the -Werror flag because the compiler gives some 
warnings that are treated as errors.

Thanks,
Alexandr.