[libomptarget] Fixed MSVC build fail caused by __attribute__((used)).

[grokos]

LGTM, thanks!

[vzakhari]

Fixed clang-format remarks.

openmp/libomptarget/include/Debug.h

enum OpenMPInfoType : uint32_t {
   // Dump the contents of the device pointer map at kernel exit or failure.
   OMP_INFOTYPE_DUMP_TABLE = 0x0004,
   // Print kernel information from target device plugins.
   OMP_INFOTYPE_PLUGIN_KERNEL = 0x0010,
   // Enable every flag.
   OMP_INFOTYPE_ALL = 0xffffffff,
 };
 
+#define GCC_VERSION                                                            \
+  (__GNUC__ * 10000 + __GNUC_MINOR__ * 100 + __GNUC_PATCHLEVEL__)
+
+#if !defined(__clang__) && defined(__GNUC__) && GCC_VERSION < 70100
+#define USED __attribute__((used))
+#else
+#define USED
+#endif
+
 // Add __attribute__((used)) to work around a bug in gcc 5/6.
-static inline uint32_t __attribute__((used)) getInfoLevel() {
+USED static inline uint32_t getInfoLevel() {
   static uint32_t InfoLevel = 0;
   static std::once_flag Flag{};
   std::call_once(Flag, []() {
     if (char *EnvStr = getenv("LIBOMPTARGET_INFO"))
       InfoLevel = std::stoi(EnvStr);
   });
 
   return InfoLevel;
 }
 
 // Add __attribute__((used)) to work around a bug in gcc 5/6.
-static inline uint32_t __attribute__((used)) getDebugLevel() {
+USED static inline uint32_t getDebugLevel() {
   static uint32_t DebugLevel = 0;
   static std::once_flag Flag{};
   std::call_once(Flag, []() {
     if (char *EnvStr = getenv("LIBOMPTARGET_DEBUG"))
       DebugLevel = std::stoi(EnvStr);
   });
 
   return DebugLevel;
 }
 
+#undef USED
+#undef GCC_VERSION
+
 #ifndef __STDC_FORMAT_MACROS
 #define __STDC_FORMAT_MACROS
 #endif
 #include <inttypes.h>
 #undef __STDC_FORMAT_MACROS
 
 #define DPxMOD "0x%0*" PRIxPTR
 #define DPxPTR(ptr) ((int)(2 * sizeof(uintptr_t))), ((uintptr_t)(ptr))