[PATCH] Revert 'Fix logic error in _AC_PROG_LEX_YYTEXT_DECL (#109320)'

[Ross Burton]

From: Ross Burton <ross.burton@arm.com>

Commit 8173e5, 'Fix logic error in _AC_PROG_LEX_YYTEXT_DECL (#109320)',
causes AC_PROG_LEX to always fail when searching for a lex library.
---
 lib/autoconf/programs.m4 | 21 ++++++++-------------
 1 file changed, 8 insertions(+), 13 deletions(-)

diff --git a/lib/autoconf/programs.m4 b/lib/autoconf/programs.m4
index 9deb62e8..006c0b66 100644
--- a/lib/autoconf/programs.m4
+++ b/lib/autoconf/programs.m4
@@ -741,7 +741,7 @@ main (void)
 }
 ]_ACEOF
 _AC_DO_VAR(LEX conftest.l)
-AC_CACHE_CHECK([for lex output file root], [ac_cv_prog_lex_root], [
+AC_CACHE_CHECK([lex output file root], [ac_cv_prog_lex_root], [
 if test -f lex.yy.c; then
   ac_cv_prog_lex_root=lex.yy
 elif test -f lexyy.c; then
@@ -751,25 +751,20 @@ else
 fi])
 AC_SUBST([LEX_OUTPUT_ROOT], [$ac_cv_prog_lex_root])dnl
 
-AS_VAR_SET_IF([LEXLIB], [], [
-  AC_CACHE_CHECK([for lex library], [ac_cv_lib_lex], [
-    ac_cv_lib_lex='not found'
+if ${LEXLIB+false} :; then
+  AC_CACHE_CHECK([lex library], [ac_cv_lib_lex], [
     ac_save_LIBS=$LIBS
+    ac_cv_lib_lex='none needed'
     for ac_lib in '' -lfl -ll; do
       LIBS="$ac_lib $ac_save_LIBS"
       AC_LINK_IFELSE([AC_LANG_DEFINES_PROVIDED[`cat $LEX_OUTPUT_ROOT.c`]],
-       [ac_cv_lib_lex="${ac_lib:-none needed}"
-         break])
+       [ac_cv_lib_lex=$ac_lib])
+      test "$ac_cv_lib_lex" != 'none needed' && break
     done
     LIBS=$ac_save_LIBS
   ])
-  AS_IF(
-     [test "$ac_cv_lib_lex" = 'not found'],
-       [AC_MSG_ERROR([required lex library not found])],
-     [test "$ac_cv_lib_lex" = 'none needed'],
-        [LEXLIB=''],
-       [LEXLIB=$ac_cv_lib_lex])
-])
+  test "$ac_cv_lib_lex" != 'none needed' && LEXLIB=$ac_cv_lib_lex
+fi
 AC_SUBST(LEXLIB)
 
 AC_CACHE_CHECK(whether yytext is a pointer, ac_cv_prog_lex_yytext_pointer,
-- 
2.26.2