build: flex.m4.

* m4/flex.m4: New.
An exact copy of what is in Autoconf currently.

m4/flex.m4

@@ -0,0 +1,93 @@
+# flex.m4 serial 1
+# Copyright (C) 2012 Free Software Foundation, Inc.
+# This file is free software; the Free Software Foundation
+# gives unlimited permission to copy and/or distribute it,
+# with or without modifications, as long as this notice is preserved.
+
+# AC_PROG_LEX
+# -----------
+# Look for flex or lex.  Set its associated library to LEXLIB.
+# Check if lex declares yytext as a char * by default, not a char[].
+AN_MAKEVAR([LEX],  [AC_PROG_LEX])
+AN_PROGRAM([lex],  [AC_PROG_LEX])
+AN_PROGRAM([flex], [AC_PROG_LEX])
+AC_DEFUN_ONCE([AC_PROG_LEX],
+[AC_CHECK_PROGS(LEX, flex lex, :)
+if test "x$LEX" != "x:"; then
+  _AC_PROG_LEX_YYTEXT_DECL
+fi])
+
+
+# _AC_PROG_LEX_YYTEXT_DECL
+# ------------------------
+# Check for the Lex output root, the Lex library, and whether Lex
+# declares yytext as a char * by default.
+m4_define([_AC_PROG_LEX_YYTEXT_DECL],
+[cat >conftest.l <<_ACEOF[
+%%
+a { ECHO; }
+b { REJECT; }
+c { yymore (); }
+d { yyless (1); }
+e { /* IRIX 6.5 flex 2.5.4 underquotes its yyless argument.  */
+    yyless ((input () != 0)); }
+f { unput (yytext[0]); }
+. { BEGIN INITIAL; }
+%%
+#ifdef YYTEXT_POINTER
+extern char *yytext;
+#endif
+int
+main (void)
+{
+  return ! yylex () + ! yywrap ();
+}
+]_ACEOF
+_AC_DO_VAR(LEX conftest.l)
+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
+  ac_cv_prog_lex_root=lexyy
+else
+  AC_MSG_ERROR([cannot find output from $LEX; giving up])
+fi])
+AC_SUBST([LEX_OUTPUT_ROOT], [$ac_cv_prog_lex_root])dnl
+
+if test -z "${LEXLIB+set}"; then
+  AC_CACHE_CHECK([lex library], [ac_cv_lib_lex], [
+    ac_save_LIBS=$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])
+      test "$ac_cv_lib_lex" != 'none needed' && break
+    done
+    LIBS=$ac_save_LIBS
+  ])
+  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,
+[# POSIX says lex can declare yytext either as a pointer or an array; the
+# default is implementation-dependent.  Figure out which it is, since
+# not all implementations provide the %pointer and %array declarations.
+ac_cv_prog_lex_yytext_pointer=no
+ac_save_LIBS=$LIBS
+LIBS="$LEXLIB $ac_save_LIBS"
+AC_LINK_IFELSE([AC_LANG_DEFINES_PROVIDED
+  [#define YYTEXT_POINTER 1
+`cat $LEX_OUTPUT_ROOT.c`]],
+  [ac_cv_prog_lex_yytext_pointer=yes])
+LIBS=$ac_save_LIBS
+])
+dnl
+if test $ac_cv_prog_lex_yytext_pointer = yes; then
+  AC_DEFINE(YYTEXT_POINTER, 1,
+	    [Define to 1 if `lex' declares `yytext' as a `char *' by default,
+	     not a `char[]'.])
+fi
+rm -f conftest.l $LEX_OUTPUT_ROOT.c
+])# _AC_PROG_LEX_YYTEXT_DECL