bpo-38527: fix configure script for Solaris (GH-16845)

On Solaris, the regular "grep" command may be an old version that fails to search a binary file. We need to use the correct command (ggrep, in our case), which is found by the configure script earlier.

Automerge-Triggered-By: @pablogsal

Author: wiggin15

Misc/NEWS.d/next/Build/2020-03-28-10-43-09.bpo-38527.fqCRgD.rst

@@ -0,0 +1,2 @@
+Fix configure check on Solaris for "float word ordering": sometimes, the correct "grep" command was not being used.
+Patch by Arnon Yaari.

configure

@@ -14340,10 +14340,10 @@ _ACEOF
 if ac_fn_c_try_compile "$LINENO"; then :
 
 
-if grep noonsees conftest.$ac_objext >/dev/null ; then
+if $GREP noonsees conftest.$ac_objext >/dev/null ; then
   ax_cv_c_float_words_bigendian=yes
 fi
-if grep seesnoon conftest.$ac_objext >/dev/null ; then
+if $GREP seesnoon conftest.$ac_objext >/dev/null ; then
   if test "$ax_cv_c_float_words_bigendian" = unknown; then
     ax_cv_c_float_words_bigendian=no
   else

m4/ax_c_float_words_bigendian.m4

@@ -49,10 +49,10 @@ double d = 909042349670368103374704789055050114762116927356156320147971208440534
 
 ]])], [
 
-if grep noonsees conftest.$ac_objext >/dev/null ; then
+if $GREP noonsees conftest.$ac_objext >/dev/null ; then
   ax_cv_c_float_words_bigendian=yes
 fi
-if grep seesnoon conftest.$ac_objext >/dev/null ; then
+if $GREP seesnoon conftest.$ac_objext >/dev/null ; then
   if test "$ax_cv_c_float_words_bigendian" = unknown; then
     ax_cv_c_float_words_bigendian=no
   else