svn version of valgrind uses #! @PERL@ for several perl
scripts. However, PERL in autoconf doesn't distinguish
host perl and target perl, causing STAGING_DIR_NATIVE be
written in the output scripts.
This causes unrunnable scripts, and fails FILERDEPENDS
mechanism (thus also do_rootfs_rpm).
Uses /usr/bin/perl instead to fix it.
Signed-off-by: Qing He <qing.he@intel.com>