testsuite: Support detection of Intel compilers via test_compiler_version.

Add Intel specific preprocessor macros to query the version of the compiler.

2016-04-18  Bernhard Heckel  <bernhard.heckel@intel.com>

gdb/Testsuite/Changelog:
	* lib/compiler.c: Add Intel specific preprocessor macros.
	* lib/compiler.cc: Likewise.