Exclude -x flags

When invoked with a -x flag under gcc, recc should fall back to local compilation for most cases.

The following languages are supported by gcc:

c  c-header  cpp-output
c++  c++-header  c++-system-header c++-user-header c++-cpp-output
objective-c  objective-c-header  objective-c-cpp-output
objective-c++ objective-c++-header objective-c++-cpp-output
assembler  assembler-with-cpp
ada
d
f77  f77-cpp-input f95  f95-cpp-input
go
brig

For all of these except c and c++, recc should perform local compilation.