fputc, fwrite tests: Avoid test failure on MSVC.

fputc, fwrite tests: Avoid test failure on MSVC.

* tests/test-fgetc.c: Include msvc-inval.h.
(main): Invoke gl_msvc_inval_ensure_handler.
* tests/test-fputc.c: Include msvc-inval.h.
(main): Invoke gl_msvc_inval_ensure_handler.
* tests/test-fread.c: Include msvc-inval.h.
(main): Invoke gl_msvc_inval_ensure_handler.
* tests/test-fwrite.c: Include msvc-inval.h.
(main): Invoke gl_msvc_inval_ensure_handler.
* modules/fgetc-tests (Depends-on): Add msvc-inval.
* modules/fputc-tests (Depends-on): Likewise.
* modules/fread-tests (Depends-on): Likewise.
* modules/fwrite-tests (Depends-on): Likewise.