[glibc] float128: use builtin_signbitf128 always

[Paul E. Murphy <murphyp@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=a49e56a945972186a829ca3ad7dec7fb9c923488

commit a49e56a945972186a829ca3ad7dec7fb9c923488
Author: Paul E. Murphy <murphyp@linux.vnet.ibm.com>
Date:   Tue Apr 7 16:20:35 2020 -0500

    float128: use builtin_signbitf128 always
    
    The minimum GCC version has been raised to 6.2 for building
    glibc.  Therefore, follow the advice inside the implementation
    and remove the GCC < 6 codepath.
    
    Likewise, remove the hidden_proto as all internal usages should
    inline now.

Diff:
---
 include/math.h                           |  1 -
 sysdeps/ieee754/float128/s_signbitf128.c | 19 +------------------
 2 files changed, 1 insertion(+), 19 deletions(-)

diff --git a/include/math.h b/include/math.h
index 3979c47400..e1c2a4eb64 100644
--- a/include/math.h
+++ b/include/math.h
@@ -29,7 +29,6 @@ hidden_proto (__isnanl)
 hidden_proto (__finitef128)
 hidden_proto (__isinff128)
 hidden_proto (__isnanf128)
-hidden_proto (__signbitf128)
 #  endif
 # endif
 
diff --git a/sysdeps/ieee754/float128/s_signbitf128.c b/sysdeps/ieee754/float128/s_signbitf128.c
index 1fc00658f8..c2a1097db6 100644
--- a/sysdeps/ieee754/float128/s_signbitf128.c
+++ b/sysdeps/ieee754/float128/s_signbitf128.c
@@ -17,21 +17,4 @@
    <https://www.gnu.org/licenses/>.  */
 
 #include <float128_private.h>
-#include <math.h>
-#include <math_private.h>
-
-/* Once GCC >= 6.0 is required for building glibc, this implementation can
-   be removed and replaced with an inclusion of ldbl-128/s_signbitl.c.  */
-int
-__signbitf128 (_Float128 x)
-{
-#if __GNUC_PREREQ (6, 0)
-  return __builtin_signbit (x);
-#else
-  int64_t e;
-
-  GET_FLOAT128_MSW64 (e, x);
-  return e < 0;
-#endif
-}
-hidden_def (__signbitf128)
+#include "../ldbl-128/s_signbitl.c"