Add explicit configure-time checks for perl.h and libperl.so.

Although most platforms seem to package Perl in such a way that these files
are present even in basic Perl installations, Debian does not.  Hence, make
an effort to fail during configure rather than build if --with-perl was
given and these files are lacking.  Per gripe from Josh Berkus.

Author: tglsfdc

configure

@@ -29124,6 +29124,131 @@ fi
     CPPFLAGS=$ac_save_CPPFLAGS
 fi
 
+# check for <perl.h>
+if test "$with_perl" = yes; then
+  ac_save_CPPFLAGS=$CPPFLAGS
+  CPPFLAGS="-I$perl_archlibexp/CORE $CPPFLAGS"
+  { $as_echo "$as_me:$LINENO: checking for perl.h" >&5
+$as_echo_n "checking for perl.h... " >&6; }
+if test "${ac_cv_header_perl_h+set}" = set; then
+  $as_echo_n "(cached) " >&6
+else
+  cat >conftest.$ac_ext <<_ACEOF
+/* confdefs.h.  */
+_ACEOF
+cat confdefs.h >>conftest.$ac_ext
+cat >>conftest.$ac_ext <<_ACEOF
+/* end confdefs.h.  */
+#include <EXTERN.h>
+
+#include <perl.h>
+_ACEOF
+rm -f conftest.$ac_objext
+if { (ac_try="$ac_compile"
+case "(($ac_try" in
+  *\"* | *\`* | *\\*) ac_try_echo=\$ac_try;;
+  *) ac_try_echo=$ac_try;;
+esac
+eval ac_try_echo="\"\$as_me:$LINENO: $ac_try_echo\""
+$as_echo "$ac_try_echo") >&5
+  (eval "$ac_compile") 2>conftest.er1
+  ac_status=$?
+  grep -v '^ *+' conftest.er1 >conftest.err
+  rm -f conftest.er1
+  cat conftest.err >&5
+  $as_echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); } && {
+	 test -z "$ac_c_werror_flag" ||
+	 test ! -s conftest.err
+       } && test -s conftest.$ac_objext; then
+  ac_cv_header_perl_h=yes
+else
+  $as_echo "$as_me: failed program was:" >&5
+sed 's/^/| /' conftest.$ac_ext >&5
+
+	ac_cv_header_perl_h=no
+fi
+
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+fi
+{ $as_echo "$as_me:$LINENO: result: $ac_cv_header_perl_h" >&5
+$as_echo "$ac_cv_header_perl_h" >&6; }
+if test "x$ac_cv_header_perl_h" = x""yes; then
+  :
+else
+  { { $as_echo "$as_me:$LINENO: error: header file <perl.h> is required for Perl" >&5
+$as_echo "$as_me: error: header file <perl.h> is required for Perl" >&2;}
+   { (exit 1); exit 1; }; }
+fi
+
+
+  # While we're at it, check that we can link to libperl.
+  # On most platforms, if perl.h is there then libperl.so will be too, but at
+  # this writing Debian packages them separately.  There is no known reason to
+  # waste cycles on separate probes for the Tcl or Python libraries, though.
+  pgac_save_LIBS=$LIBS
+  LIBS="$perl_embed_ldflags $LIBS"
+  { $as_echo "$as_me:$LINENO: checking for libperl" >&5
+$as_echo_n "checking for libperl... " >&6; }
+  cat >conftest.$ac_ext <<_ACEOF
+/* confdefs.h.  */
+_ACEOF
+cat confdefs.h >>conftest.$ac_ext
+cat >>conftest.$ac_ext <<_ACEOF
+/* end confdefs.h.  */
+
+#include <EXTERN.h>
+#include <perl.h>
+
+int
+main ()
+{
+perl_alloc();
+  ;
+  return 0;
+}
+_ACEOF
+rm -f conftest.$ac_objext conftest$ac_exeext
+if { (ac_try="$ac_link"
+case "(($ac_try" in
+  *\"* | *\`* | *\\*) ac_try_echo=\$ac_try;;
+  *) ac_try_echo=$ac_try;;
+esac
+eval ac_try_echo="\"\$as_me:$LINENO: $ac_try_echo\""
+$as_echo "$ac_try_echo") >&5
+  (eval "$ac_link") 2>conftest.er1
+  ac_status=$?
+  grep -v '^ *+' conftest.er1 >conftest.err
+  rm -f conftest.er1
+  cat conftest.err >&5
+  $as_echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); } && {
+	 test -z "$ac_c_werror_flag" ||
+	 test ! -s conftest.err
+       } && test -s conftest$ac_exeext && {
+	 test "$cross_compiling" = yes ||
+	 $as_test_x conftest$ac_exeext
+       }; then
+  { $as_echo "$as_me:$LINENO: result: yes" >&5
+$as_echo "yes" >&6; }
+else
+  $as_echo "$as_me: failed program was:" >&5
+sed 's/^/| /' conftest.$ac_ext >&5
+
+	{ $as_echo "$as_me:$LINENO: result: no" >&5
+$as_echo "no" >&6; }
+     { { $as_echo "$as_me:$LINENO: error: libperl library is required for Perl" >&5
+$as_echo "$as_me: error: libperl library is required for Perl" >&2;}
+   { (exit 1); exit 1; }; }
+fi
+
+rm -rf conftest.dSYM
+rm -f core conftest.err conftest.$ac_objext conftest_ipa8_conftest.oo \
+      conftest$ac_exeext conftest.$ac_ext
+  LIBS=$pgac_save_LIBS
+  CPPFLAGS=$ac_save_CPPFLAGS
+fi
+
 # check for <Python.h>
 if test "$with_python" = yes; then
   ac_save_CPPFLAGS=$CPPFLAGS

configure.in

@@ -1792,6 +1792,30 @@ if test "$with_tcl" = yes; then
     CPPFLAGS=$ac_save_CPPFLAGS
 fi
 
+# check for <perl.h>
+if test "$with_perl" = yes; then
+  ac_save_CPPFLAGS=$CPPFLAGS
+  CPPFLAGS="-I$perl_archlibexp/CORE $CPPFLAGS"
+  AC_CHECK_HEADER(perl.h, [], [AC_MSG_ERROR([header file <perl.h> is required for Perl])],
+                  [#include <EXTERN.h>])
+  # While we're at it, check that we can link to libperl.
+  # On most platforms, if perl.h is there then libperl.so will be too, but at
+  # this writing Debian packages them separately.  There is no known reason to
+  # waste cycles on separate probes for the Tcl or Python libraries, though.
+  pgac_save_LIBS=$LIBS
+  LIBS="$perl_embed_ldflags $LIBS"
+  AC_MSG_CHECKING([for libperl])
+  AC_TRY_LINK([
+#include <EXTERN.h>
+#include <perl.h>
+],  [perl_alloc();],
+    [AC_MSG_RESULT(yes)],
+    [AC_MSG_RESULT(no)
+     AC_MSG_ERROR([libperl library is required for Perl])])
+  LIBS=$pgac_save_LIBS
+  CPPFLAGS=$ac_save_CPPFLAGS
+fi
+
 # check for <Python.h>
 if test "$with_python" = yes; then
   ac_save_CPPFLAGS=$CPPFLAGS