symbol-scan.pl: do not require autotools

Makes test1119 pass when building with cmake.

configurehelp.pm is generated by configure (autotools). As cmake does
not provide a separate variable for the C preprocessor, default to cpp.
Before commit ef24ecde68a5f577a7f0f423a767620f09a0ab16 ("symbol-scan:
use configure script knowledge about how to run the C preprocessor"),
this tool would also use 'cpp'.

Signed-off-by: Peter Wu <peter@lekensteyn.nl>

tests/symbol-scan.pl

@@ -27,13 +27,23 @@
 
 use strict;
 use warnings;
+use vars qw($Cpreprocessor);
 
 #
 # configurehelp perl module is generated by configure script
 #
-use configurehelp qw(
-    $Cpreprocessor
-    );
+my $rc = eval {
+    require configurehelp;
+    configurehelp->import(qw(
+        $Cpreprocessor
+    ));
+    1;
+};
+# Set default values if configure has not generated a configurehelp.pm file.
+# This is the case with cmake.
+if (!$rc) {
+    $Cpreprocessor = 'cpp';
+}
 
 # we may get the dir root pointed out
 my $root=$ARGV[0] || ".";