[OpenMP] Fix a few build issues

Fix two build issues:

1) Recent commit 348756 accidentally included Unix clang compilers
   to use immintrin.h when only clang-cl should be using it leading
   to the following error:

openmp-llvm/runtime/src/kmp_lock.cpp:2035:25: error: always_
inline function '_xbegin' requires target feature 'rtm', but would be inlined into function
      '__kmp_test_adaptive_lock_only' that is compiled without support for 'rtm'
          kmp_uint32 status = _xbegin();
This patch changes the guard to use immintrin.h to only use clang-cl instead of all clang

2) gcc-8 gives a warning about multiline comment in kmp_runtime.cpp:
This patch just changes it to a two line comment
openmp-llvm/runtime/src/kmp_runtime.cpp:7697:8: warning: multi-line comment [-Wcomment]
 #endif // KMP_OS_LINUX || KMP_OS_DRAGONFLY || KMP_OS_FREEBSD || KMP_OS_NETBSD  \

llvm-svn: 348783

openmp/runtime/src/kmp_lock.cpp

@@ -1717,7 +1717,8 @@ static void __kmp_set_queuing_lock_flags(kmp_queuing_lock_t *lck,
 /* RTM Adaptive locks */
 
 #if (KMP_COMPILER_ICC && __INTEL_COMPILER >= 1300) ||                          \
-    (KMP_COMPILER_MSVC && _MSC_VER >= 1700) || KMP_COMPILER_CLANG
+    (KMP_COMPILER_MSVC && _MSC_VER >= 1700) ||                                 \
+    (KMP_COMPILER_CLANG && KMP_MSVC_COMPAT)
 
 #include <immintrin.h>
 #define SOFT_ABORT_MASK (_XABORT_RETRY | _XABORT_CONFLICT | _XABORT_EXPLICIT)

openmp/runtime/src/kmp_runtime.cpp

@@ -7694,8 +7694,8 @@ __kmp_determine_reduction_method(
     }
 #else
 #error "Unknown or unsupported OS"
-#endif // KMP_OS_LINUX || KMP_OS_DRAGONFLY || KMP_OS_FREEBSD || KMP_OS_NETBSD  \
-// || KMP_OS_OPENBSD || KMP_OS_WINDOWS || KMP_OS_DARWIN || KMP_OS_HURD
+#endif // KMP_OS_LINUX || KMP_OS_DRAGONFLY || KMP_OS_FREEBSD || KMP_OS_NETBSD ||
+       // KMP_OS_OPENBSD || KMP_OS_WINDOWS || KMP_OS_DARWIN || KMP_OS_HURD
 
 #elif KMP_ARCH_X86 || KMP_ARCH_ARM || KMP_ARCH_AARCH || KMP_ARCH_MIPS