gallium: Only use C++ compiler for linking when using LLVM.

Otherwise, the shared objects needlessly link against the C++ runtime
environment.
diff --git a/SConstruct b/SConstruct
index dd118df..44ac0ad 100644
--- a/SConstruct
+++ b/SConstruct
@@ -206,9 +206,7 @@
 	env.ParseConfig('llvm-config --cflags --ldflags --libs')
 	env.Append(CPPDEFINES = ['MESA_LLVM'])
 	env.Append(CXXFLAGS = ['-Wno-long-long'])
-
-# Force C++ linkage
-if env['PLATFORM'] in ('posix',):
+        # Force C++ linkage
 	env['LINK'] = env['CXX']
 
 # libGL