[OMPD] Runtime Entry Point functions for OMPD in libomp.so is mangled.

Encapsulating required OMPD and OMPT data structures and signatures within
extern "C" as per the supplementary soure file for omp-tools.h provided by
the OpenMP spec
https://github.com/OpenMP/sources/blob/main/include/omp-tools.h,
thus ensuring that the OMPD runtime entry point functions have C linkage
and are not mangled.

Author: vigbalu

openmp/runtime/src/include/omp-tools.h.var

@@ -211,6 +211,10 @@ typedef enum kmp_mutex_impl_t {
  * definitions generated from spec
  *****************************************************************************/
 
+#if defined(__cplusplus)
+extern "C" {
+#endif
+
 typedef enum ompt_callbacks_t {
   ompt_callback_thread_begin             = 1,
   ompt_callback_thread_end               = 2,
@@ -1414,4 +1418,8 @@ typedef ompt_record_ompt_t *(*ompt_get_record_ompt_t) (
 
 #define ompd_segment_none 0
 
+#if defined(__cplusplus)
+} // extern "C"
+#endif
+
 #endif /* __OMPT__ */