Change how the symbol_version_reference macro is defined

A subsequent change will require including <config.h> for defining
symbol_version_reference.  <libc-symbol.h> should not include
<config.h> for _ISOMAC, so it cannot define symbol_version_reference
anymore, but symbol_version_reference is needed <shlib-compat.h> even
for _ISOMAC.  Moving the definition of symbol_version_reference to a
separate file <libc-symver.h> makes it possible to use a single
definition for both cases.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

include/libc-symbols.h

@@ -59,19 +59,6 @@
 # define IN_MODULE (-1)
 #endif
 
-/* Use symbol_version_reference to specify the version a symbol
-   reference should link to.  Use symbol_version or
-   default_symbol_version for the definition of a versioned symbol.
-   The difference is that the latter is a no-op in non-shared
-   builds.  */
-#ifdef __ASSEMBLER__
-# define symbol_version_reference(real, name, version) \
-     .symver real, name##@##version
-#else  /* !__ASSEMBLER__ */
-# define symbol_version_reference(real, name, version) \
-  __asm__ (".symver " #real "," #name "@" #version)
-#endif
-
 #ifndef _ISOMAC
 
 /* This is defined for the compilation of all C library code.  features.h
@@ -97,6 +84,9 @@
 
 #include <config.h>
 
+/* Obtain the definition of symbol_version_reference.  */
+#include <libc-symver.h>
+
 /* When PIC is defined and SHARED isn't defined, we are building PIE
    by default.  */
 #if defined PIC && !defined SHARED

include/shlib-compat.h

@@ -21,6 +21,9 @@
 
 # include <abi-versions.h>
 
+/* Obtain the definition of symbol_version_reference.  */
+#include <libc-symver.h>
+
 /* The file abi-versions.h (generated by scripts/abi-versions.awk) defines
    symbols like `ABI_libm_GLIBC_2_0' for each version set in the source
    code for each library.  For a version set that is subsumed by a later

sysdeps/generic/libc-symver.h

@@ -0,0 +1,38 @@
+/* Symbol version management.
+   Copyright (C) 1995-2021 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+/* This file is included from <libc-symbols.h> for !_ISOMAC, and
+   unconditionally from <shlib-compat.h>.  */
+
+#ifndef _LIBC_SYMVER_H
+#define _LIBC_SYMVER_H 1
+
+/* Use symbol_version_reference to specify the version a symbol
+   reference should link to.  Use symbol_version or
+   default_symbol_version for the definition of a versioned symbol.
+   The difference is that the latter is a no-op in non-shared
+   builds.  */
+#ifdef __ASSEMBLER__
+# define symbol_version_reference(real, name, version) \
+     .symver real, name##@##version
+#else  /* !__ASSEMBLER__ */
+# define symbol_version_reference(real, name, version) \
+  __asm__ (".symver " #real "," #name "@" #version)
+#endif
+
+#endif /* _LIBC_SYMVER_H */