Fix ICC C++ compiler warnings on OS X

ICC C++ compiler icpc takes all defined macros from existing clang, so
__clang__ is defined as well for icpc, yet it does not support #pragma clang.

So prior using #pragma clang we shall check if it is not icpc compiler.

This fixes tens of warnings when using iclc, e.g.:

	lib/catch/include/internal/catch_ptr.hpp(14): warning #161: unrecognized #pragma
	  #pragma clang diagnostic push
	          ^

	In file included from lib/catch/include/internal/catch_context.h(12),
	                 from lib/catch/include/catch.hpp(26),
	                 from src/2d_strip/strip_detector_test.cpp(1):
	lib/catch/include/internal/catch_ptr.hpp(15): warning #161: unrecognized #pragma
	  #pragma clang diagnostic ignored "-Wpadded"
	          ^

	In file included from /Applications/Xcode-Beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/vector(274),
	                 from lib/catch/include/internal/catch_context.h(15),
	                 from lib/catch/include/catch.hpp(26),
	                 from src/2d_strip/strip_detector_test.cpp(1):
	lib/catch/include/internal/catch_ptr.hpp(91): warning #161: unrecognized #pragma
	  #pragma clang diagnostic pop
	          ^

	In file included from lib/catch/include/catch.hpp(39),
	                 from src/2d_strip/strip_detector_test.cpp(1):
	lib/catch/include/internal/catch_test_case_info.h(18): warning #161: unrecognized #pragma
	  #pragma clang diagnostic push
	          ^

	In file included from lib/catch/include/catch.hpp(39),
	                 from src/2d_strip/strip_detector_test.cpp(1):
	lib/catch/include/internal/catch_test_case_info.h(19): warning #161: unrecognized #pragma
	  #pragma clang diagnostic ignored "-Wpadded"
	          ^

	In file included from src/2d_strip/strip_detector_test.cpp(1):
	lib/catch/include/internal/catch_test_case_info.h(87): warning #161: unrecognized #pragma
	  #pragma clang diagnostic pop
	          ^

	In file included from src/2d_strip/strip_detector_test.cpp(5):
	lib/catch/include/internal/catch_reenable_warnings.h(12): warning #161: unrecognized #pragma
	  #pragma clang diagnostic pop