getprogname: Avoid using HAVE_* macros in *.in.h files. * m4/stdlib_h.m4 (gl_STDLIB_H_DEFAULTS): Initialize HAVE_DECL_PROGRAM_INVOCATION_NAME. * m4/getprogname.m4 (gl_FUNC_GETPROGNAME): Require gl_STDLIB_H_DEFAULTS and gl_USE_SYSTEM_EXTENSIONS. Set HAVE_DECL_PROGRAM_INVOCATION_NAME. * modules/stdlib (Makefile.am): Substitute HAVE_DECL_PROGRAM_INVOCATION_NAME. * lib/stdlib.in.h (getprogname): Test HAVE_DECL_PROGRAM_INVOCATION_NAME as an Autoconf variable.