module: make MODULE_SYMBOL_PREFIX into a CONFIG option

The next commit will require the use of MODULE_SYMBOL_PREFIX in
.tmp_exports-asm.S.  Currently it is mixed in with C structure
definitions in "asm/module.h".  Move the definition of this arch option
into Kconfig, so it can be easily accessed by any code.

This also lets modpost.c use the same definition.  Previously modpost
relied on a hardcoded list of architectures in mk_elfconfig.c.

A build test for blackfin, one of the two MODULE_SYMBOL_PREFIX archs,
showed the generated code was unchanged.  vmlinux was identical save
for build ids, and an apparently randomized suffix on a single "__key"
symbol in the kallsyms data).

Signed-off-by: Alan Jenkins <alan-jenkins@tuffmail.co.uk>
Acked-by: Mike Frysinger <vapier@gentoo.org> (blackfin)
CC: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

arch/blackfin/Kconfig

@@ -5,6 +5,10 @@
 
 mainmenu "Blackfin Kernel Configuration"
 
+config SYMBOL_PREFIX
+	string
+	default "_"
+
 config MMU
 	def_bool n
 

arch/blackfin/include/asm/module.h

@@ -7,8 +7,6 @@
 #ifndef _ASM_BFIN_MODULE_H
 #define _ASM_BFIN_MODULE_H
 
-#define MODULE_SYMBOL_PREFIX "_"
-
 #define Elf_Shdr        Elf32_Shdr
 #define Elf_Sym         Elf32_Sym
 #define Elf_Ehdr        Elf32_Ehdr

arch/blackfin/kernel/vmlinux.lds.S

@@ -4,8 +4,6 @@
  * Licensed under the GPL-2 or later
  */
 
-#define VMLINUX_SYMBOL(_sym_) _##_sym_
-
 #include <asm-generic/vmlinux.lds.h>
 #include <asm/mem_map.h>
 #include <asm/page.h>