stdio: simplify by moving files to printf-posix, sigpipe

stdio: simplify by moving files to printf-posix, sigpipe

* m4/stdio_h.m4 (gl_STDIO_H): Do not require gl_ASM_SYMBOL_PREFIX,
since this symbol is needed only if printf is replaced.
* m4/printf-posix-rpl.m4 (gl_REPLACE_PRINTF):
Require gl_ASM_SYMBOL_PREFIX.
* modules/printf-posix (Files): Add m4/asm-underscore.m4.
* modules/sigpipe (Files): Likewise.  Also, add m4/stdio-write.c.
(Depends-on): Add 'raise'.
(configure.ac): Require gl_ASM_SYMBOL_PREFIX.
* modules/stdio (Files): Remove lib/stdio-write.c,
m4/asm-underscore.m4.
(Depends-on): Remove 'raise'.