libgomp: Fix up omp_target_memset-3.c test for C++ [PR120444]

libgomp: Fix up omp_target_memset-3.c test for C++ [PR120444]

The test PASSes for C, but FAILs for C++:
.../libgomp.c-c++-common/omp_target_memset-3.c: In function 'void test_it(void*, int, size_t)':
.../libgomp.c-c++-common/omp_target_memset-3.c:31:7: warning: pointer of type 'void *' used in arithmetic [-Wpointer-arith]
.../libgomp.c-c++-common/omp_target_memset-3.c:33:13: error: invalid conversion from 'void*' to 'int8_t*' {aka 'signed char*'} [-fpermissive]
.../libgomp.c-c++-common/omp_target_memset-3.c:10:19: note: initializing argument 1 of 'void init_val(int8_t*, int, size_t)'
.../libgomp.c-c++-common/omp_target_memset-3.c:37:14: error: invalid conversion from 'void*' to 'int8_t*' {aka 'signed char*'} [-fpermissive]
.../libgomp.c-c++-common/omp_target_memset-3.c:17:20: note: initializing argument 1 of 'void check_val(int8_t*, int, size_t)'
.../libgomp.c-c++-common/omp_target_memset-3.c:38:18: warning: pointer of type 'void *' used in arithmetic [-Wpointer-arith]
.../libgomp.c-c++-common/omp_target_memset-3.c:38:18: error: invalid conversion from 'void*' to 'int8_t*' {aka 'signed char*'} [-fpermissive]
.../libgomp.c-c++-common/omp_target_memset-3.c:17:20: note: initializing argument 1 of 'void check_val(int8_t*, int, size_t)'
.../libgomp.c-c++-common/omp_target_memset-3.c: In function 'int main()':
.../libgomp.c-c++-common/omp_target_memset-3.c:46:7: warning: pointer of type 'void *' used in arithmetic [-Wpointer-arith]

The following two-liner fixes that, tested on x86_64-linux and i686-linux.

2025-06-03  Jakub Jelinek  <jakub@redhat.com>

	PR libgomp/120444
	* testsuite/libgomp.c-c++-common/omp_target_memset-3.c (test_it):
	Change ptr argument type from void * to int8_t *.
	(main): Change ptr variable type from void * to int8_t * and cast
	omp_target_alloc result to the latter type.

(cherry picked from commit a8c03f056f4070a618bc59afcae2290cf21456ea)