s390: use $READELF

We already check for it in root configure.ac with AC_CHECK_TOOL. Let's
use the result.

Tested on s390x-ibm-linux-gnu.

Signed-off-by: Sam James <sam@gentoo.org>
Reviewed-by: Stefan Liebler <stli@linux.ibm.com>

sysdeps/s390/s390-64/configure

@@ -50,7 +50,7 @@ EOF
   ac_status=$?
   $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
   test $ac_status = 0; }; } \
-     && { ac_try='! readelf -Wr conftest | grep R_390_TLS_TPOFF'
+     && { ac_try='! $READELF -Wr conftest | grep R_390_TLS_TPOFF'
   { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
   (eval $ac_try) 2>&5
   ac_status=$?

sysdeps/s390/s390-64/configure.ac

@@ -31,7 +31,7 @@ EOF
   if AC_TRY_COMMAND([${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS -fPIE -c conftest1.c -o conftest1.o]) \
      && AC_TRY_COMMAND([${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS -fPIE -c conftest2.c -o conftest2.o]) \
      && AC_TRY_COMMAND([${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS -pie -o conftest conftest1.o conftest2.o]) \
-     && AC_TRY_COMMAND([! readelf -Wr conftest | grep R_390_TLS_TPOFF])
+     && AC_TRY_COMMAND([! $READELF -Wr conftest | grep R_390_TLS_TPOFF])
   then
     libc_cv_s390x_staticpie_req=yes
   fi