[libgomp, nvptx] Fix libgomp.c/target-5.c compilation

[libgomp, nvptx] Fix libgomp.c/target-5.c compilation

Libgomp test-case libgomp.c/target-5.c is failing to compile when building for
x86_64 with nvptx accelerator due to missing:
- getpid
- gethostname
- isatty (pulled in by fwrite)
in the nvptx newlib.

This patch fixes the build failure by:
- adding a function gomp_print_string which limits the use of fwrite to a single
  location (in affinity-fmt.c), and
- creating an nvptx version of affinity-fmt.c, which:
  - overrides the configure test results HAVE_GETPID and HAVE_GETHOSTNAME, and
  - implements fwrite using write.

Build and reg-tested on x86_64 with nvptx accelerator.

2018-12-13  Tom de Vries  <tdevries@suse.de>

	* affinity-fmt.c (gomp_print_string): New function, factored out of ...
	(omp_display_affinity, gomp_display_affinity_thread): ... here, and ...
	* fortran.c (omp_display_affinity_): ... here.
	* libgomp.h (gomp_print_string): Declare.
	* config/nvptx/affinity-fmt.c: New file.  Include affinity-fmt.c,
	undefining HAVE_GETPID and HAVE_GETHOSTNAME, and mapping fwrite to
	write.

From-SVN: r267100