build: look for Perl in configure.

Bison uses "/usr/bin/perl" or "perl" in several places, and it does
not appear to be a problem.  But, at least to make it simpler to
change PERL on the make command line, check for perl in configure.

* configure.ac (PERL): New.
* doc/Doxyfile.in, doc/local.mk, examples/local.mk,
* tests/bison.in: Use it.

configure.ac

@@ -122,6 +122,10 @@ AC_PROG_GNU_M4
 AC_DEFINE_UNQUOTED([M4], ["$M4"], [Define to the GNU M4 executable name.])
 AC_DEFINE_UNQUOTED([M4_GNU_OPTION], ["$M4_GNU"], [Define to "-g" if GNU M4
 supports -g, otherwise to "".])
+AC_PATH_PROG([PERL], [perl])
+if test -z "$PERL"; then
+   AC_MSG_ERROR([perl not found])
+fi
 AM_MISSING_PROG([HELP2MAN], [help2man])
 AC_PATH_PROG([XSLTPROC], [xsltproc])
 AC_SUBST([XSLTPROC])

doc/Doxyfile.in

@@ -1579,7 +1579,7 @@ EXTERNAL_GROUPS        = YES
 # The PERL_PATH should be the absolute path and name of the perl script
 # interpreter (i.e. the result of `which perl').
 
-PERL_PATH              = /usr/bin/perl
+PERL_PATH              = @PERL@
 
 #---------------------------------------------------------------------------
 # Configuration options related to the dot tool

doc/local.mk

@@ -36,7 +36,7 @@ $(CROSS_OPTIONS_TEXI): doc/bison.help $(CROSS_OPTIONS_PL)
 	$(AM_V_GEN){ test ! -f $@ || cat $@; } >$@~
 	$(AM_V_at)test ! -f $@.tmp || rm -f $@.tmp
 	$(AM_V_at)src/bison$(EXEEXT) --help |				 \
-	  perl $(CROSS_OPTIONS_PL) $(top_srcdir)/src/scan-gram.l >$@.tmp
+	  $(PERL) $(CROSS_OPTIONS_PL) $(top_srcdir)/src/scan-gram.l >$@.tmp
 	$(AM_V_at)diff -u $@~ $@.tmp || true
 	$(AM_V_at)mv $@.tmp $@
 MAINTAINERCLEANFILES = $(CROSS_OPTIONS_TEXI)
@@ -127,6 +127,7 @@ html-local: doc/Doxyfile
 
 edit = sed -e 's,@PACKAGE_NAME\@,$(PACKAGE_NAME),g' \
 	   -e 's,@PACKAGE_VERSION\@,$(PACKAGE_VERSION),g' \
+	   -e 's,@PERL\@,$(PERL),g' \
 	   -e 's,@top_builddir\@,$(top_builddir),g' \
 	   -e 's,@top_srcdir\@,$(top_srcdir),g'
 

examples/local.mk

@@ -22,7 +22,6 @@ TEST_LOG_COMPILER = $(top_srcdir)/examples/test
 
 doc = $(top_srcdir)/doc/bison.texinfo
 extexi = $(top_srcdir)/examples/extexi
-PERL = perl
 extract = VERSION="$(VERSION)" $(PERL) -f $(extexi) $(doc) --
 extracted =
 CLEANFILES += $(extracted) examples/extracted.stamp

tests/bison.in

@@ -19,6 +19,7 @@
 
 abs_top_srcdir='@abs_top_srcdir@'
 abs_top_builddir='@abs_top_builddir@'
+: ${PERL='@perl@'}
 
 # Use the shipped files, not those installed.
 BISON_PKGDATADIR=$abs_top_srcdir/data
@@ -34,7 +35,6 @@ for i
 do
   case $i in
     */src/parse-gram.y)
-    : ${PERL=perl}
     if $PERL --version >/dev/null; then
       # We are called by ylwrap which still uses y.tab.*, and
       # post-processes the synclines on y.tab.c itself.  Don't let it