We use gcc which doesn't support -flags. So remove it.

--- zlib-1.2.12/configure.orig	2022-03-28 01:39:42.000000000 +0000
+++ zlib-1.2.12/configure	2022-03-31 14:25:13.873964238 +0000
@@ -307,8 +307,7 @@
          if test $build64 -eq 1; then
              # old versions of SunPRO/Workshop/Studio don't support -m64,
              # but newer ones do.  Check for it.
-             flag64=`$CC -flags | egrep -- '^-m64'`
-             if test x"$flag64" != x"" ; then
+             if true ; then
                  CFLAGS="${CFLAGS} -m64"
                  SFLAGS="${SFLAGS} -m64"
              else