Fix LEXLIB and YYTEXT_POINTER with IRIX 6.5 flex 2.5.4.

[Ralf Wildenhues]

http://autobuild.josefsson.org/automake/log-201101181921817456000.txt
On IRIX, the code from AC_PROG_LEX sees something like this:

$ cc -o conf lex.yy.c -ll
cc-1042 cc: ERROR File = conf.l, Line = 6
  The types of operands "char *" and "int" are incompatible.

  { yyless (input () != 0); }
    ^

caused by something ugly like this:

| #define yyless(n) \
|         do \
|                 { \
|                 /* Undo effects of setting up yytext. */ \
|                 *yy_cp = yy_hold_char; \
|                 YY_RESTORE_YY_MORE_OFFSET \
|                 yy_c_buf_p = yy_cp = yy_bp + n - YY_MORE_ADJ; \
|                 YY_DO_BEFORE_ACTION; /* set up yytext again */ \
|                 } \
|         while ( 0 )
| 
[...]
| /* Redefine yyless() so it works in section 3 code. */
| 
| #undef yyless
| #define yyless(n) \
|         do \
|                 { \
|                 /* Undo effects of setting up yytext. */ \
|                 yytext[yyleng] = yy_hold_char; \
|                 yy_c_buf_p = yytext + n; \
|                 yy_hold_char = *yy_c_buf_p; \
|                 *yy_c_buf_p = '\0'; \
|                 yyleng = n; \
|                 } \
|         while ( 0 )

which in turn causes an Automake test failure.

OK to push the fix below, even if it's to work around decade
old bugs?

Thanks,
Ralf

    Fix LEXLIB and YYTEXT_POINTER with IRIX 6.5 flex 2.5.4.
    
    * lib/autoconf/programs.m4 (_AC_PROG_LEX_YYTEXT_DECL):
    Overquote nontrivial yyless argument, to compensate for
    underquoted macro definition in IRIX 6.5 flex 2.5.4
    leading to compile failure due to incompatible operands.
    Fixes Automake silent-lex-generic.test failure.

diff --git a/lib/autoconf/programs.m4 b/lib/autoconf/programs.m4
index 0def8b2..fb3d8b9 100644
--- a/lib/autoconf/programs.m4
+++ b/lib/autoconf/programs.m4
@@ -724,7 +724,8 @@ a { ECHO; }
 b { REJECT; }
 c { yymore (); }
 d { yyless (1); }
-e { yyless (input () != 0); }
+e { /* IRIX 6.5 flex 2.5.4 underquotes its yyless argument.  */
+    yyless ((input () != 0)); }
 f { unput (yytext[0]); }
 . { BEGIN INITIAL; }
 %%