[gcc r13-3763] libstdc++: Fix up libstdc++ build against glibc 2.25 or older [PR107562]

[Jakub Jelinek <jakub@gcc.gnu.org>]

https://gcc.gnu.org/g:b457b779427b0f7b3fbac447811c9c52db5bc79e

commit r13-3763-gb457b779427b0f7b3fbac447811c9c52db5bc79e
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Tue Nov 8 00:35:09 2022 +0100

    libstdc++: Fix up libstdc++ build against glibc 2.25 or older [PR107562]
    
    On Mon, Nov 07, 2022 at 05:48:42PM +0000, Jonathan Wakely wrote:
    > On Mon, 7 Nov 2022 at 16:11, Joseph Myers <joseph@codesourcery.com> wrote:
    > >
    > > On Wed, 2 Nov 2022, Jakub Jelinek via Gcc-patches wrote:
    > >
    > > > APIs.  So that one can build gcc against older glibc and then compile
    > > > user programs on newer glibc, the patch uses weak references unless
    > > > gcc is compiled against glibc 2.26+.  strfromf128 unfortunately can't
    > >
    > > This support for older glibc doesn't actually seem to be working, on an
    > > older system with glibc 2.19 I'm seeing
    > >
    > > /scratch/jmyers/fsf/gcc-mainline/libstdc++-v3/src/c++17/floating_to_chars.cc:52:3: error: expected initializer before '__asm'
    > >    52 |   __asm ("strfromf128");
    > >       |   ^~~~~
    > >
    > > and a series of subsequent errors.
    >
    > This seems to "fix" it (not sure if it's right though):
    >
    > #ifndef _GLIBCXX_HAVE_FLOAT128_MATH
    > extern "C" _Float128 __strtof128(const char*, char**)
    >  __attribute__((__weak__));
    > #endif
    > extern "C" _Float128 __strtof128(const char*, char**)
    >  __asm ("strtof128");
    
    It is, but floating_from_chars.cc has the same problem,
    and I think we can avoid the duplication, like this:
    
    2022-11-08  Jakub Jelinek  <jakub@redhat.com>
    
            PR libstdc++/107562
            * src/c++17/floating_from_chars.cc (__strtof128): Put __asm before
            __attribute__.
            * src/c++17/floating_to_chars.cc (__strfromf128): Likewise.

Diff:
---
 libstdc++-v3/src/c++17/floating_from_chars.cc | 3 ++-
 libstdc++-v3/src/c++17/floating_to_chars.cc   | 3 ++-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/libstdc++-v3/src/c++17/floating_from_chars.cc b/libstdc++-v3/src/c++17/floating_from_chars.cc
index 11a9be68770..29eb4634e9d 100644
--- a/libstdc++-v3/src/c++17/floating_from_chars.cc
+++ b/libstdc++-v3/src/c++17/floating_from_chars.cc
@@ -63,10 +63,11 @@ extern "C" __ieee128 __strtoieee128(const char*, char**);
       && defined(__GLIBC_PREREQ)
 #define USE_STRTOF128_FOR_FROM_CHARS 1
 extern "C" _Float128 __strtof128(const char*, char**)
+  __asm ("strtof128")
 #ifndef _GLIBCXX_HAVE_FLOAT128_MATH
   __attribute__((__weak__))
 #endif
-  __asm ("strtof128");
+  ;
 #endif
 
 #if _GLIBCXX_FLOAT_IS_IEEE_BINARY32 && _GLIBCXX_DOUBLE_IS_IEEE_BINARY64 \
diff --git a/libstdc++-v3/src/c++17/floating_to_chars.cc b/libstdc++-v3/src/c++17/floating_to_chars.cc
index d6be6465b12..afce8d74c12 100644
--- a/libstdc++-v3/src/c++17/floating_to_chars.cc
+++ b/libstdc++-v3/src/c++17/floating_to_chars.cc
@@ -46,10 +46,11 @@ extern "C" int __sprintfieee128(char*, const char*, ...);
 #elif __FLT128_MANT_DIG__ == 113 && __LDBL_MANT_DIG__ != 113 \
       && defined(__GLIBC_PREREQ)
 extern "C" int __strfromf128(char*, size_t, const char*, _Float128)
+  __asm ("strfromf128")
 #ifndef _GLIBCXX_HAVE_FLOAT128_MATH
   __attribute__((__weak__))
 #endif
-  __asm ("strfromf128");
+  ;
 #endif
 
 // This implementation crucially assumes float/double have the