[OpenMP] Move header inclusion out of 'extern "C"'

[Hahnfeld]

Summary

This leads to problems when compiling C++ code with libc++ for Nvidia GPUs
because Clang now uses wrappers for math functions that might include
C++ templates not allowed in 'extern "C"'.

[jdoerfert]

LGTM

[Hahnfeld]

Rebase. (clever git even did the merge for me!)

[AndreyChurbanov]

LGTM

[Hahnfeld]

Committed in rL366229 (but made a typo)

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

 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 
 #ifndef __OMP_H
 #   define __OMP_H
 
+#   include <stdlib.h>
+#   include <stdint.h>
+
 #   define KMP_VERSION_MAJOR    @LIBOMP_VERSION_MAJOR@
 #   define KMP_VERSION_MINOR    @LIBOMP_VERSION_MINOR@
 #   define KMP_VERSION_BUILD    @LIBOMP_VERSION_BUILD@
 #   define KMP_BUILD_DATE       "@LIBOMP_BUILD_DATE@"
 
 #   ifdef __cplusplus
     extern "C" {
 #   endif
#   endif
     extern int  __KAI_KMPC_CONVENTION  omp_get_default_device (void);
     extern void __KAI_KMPC_CONVENTION  omp_set_default_device (int);
     extern int  __KAI_KMPC_CONVENTION  omp_is_initial_device (void);
     extern int  __KAI_KMPC_CONVENTION  omp_get_num_devices (void);
     extern int  __KAI_KMPC_CONVENTION  omp_get_num_teams (void);
     extern int  __KAI_KMPC_CONVENTION  omp_get_team_num (void);
     extern int  __KAI_KMPC_CONVENTION  omp_get_cancellation (void);
 
-#   include <stdlib.h>
-#   include <stdint.h>
     /* OpenMP 4.5 */
     extern int   __KAI_KMPC_CONVENTION  omp_get_initial_device (void);
     extern void* __KAI_KMPC_CONVENTION  omp_target_alloc(size_t, int);
     extern void  __KAI_KMPC_CONVENTION  omp_target_free(void *, int);
     extern int   __KAI_KMPC_CONVENTION  omp_target_is_present(void *, int);
     extern int   __KAI_KMPC_CONVENTION  omp_target_memcpy(void *, void *, size_t, size_t, size_t, int, int);
     extern int   __KAI_KMPC_CONVENTION  omp_target_memcpy_rect(void *, void *, size_t, int, const size_t *,
                                             const size_t *, const size_t *, const size_t *, const size_t *, int, int);