[OE-core] PERL and FULLPERL from MakeMaker.pm

[Tian, Kevin]

Hi, all,

I just found that several perl-based projects (e.g. sgmlspl and git) failed to find
ExtUtils modules, when sstate cache is used for perl-native while original build 
directory generating sstate packages have been deleted.

We have a perl wrapper to make sure @INC correctly including current build
sysroot, which however doesn't solve the problem seen here.

Those projects make use of MakeMaker.pm to generate their Makefiles on the
fly, while MakeMaker.pm generates below lines:

PERL = /media/builds-0/demo-0309/tmp/sysroots/x86_64-linux/usr/bin/perl.real
FULLPERL =
/media/builds-0/demo-0309/tmp/sysroots/x86_64-linux/usr/bin/perl.real

I can work around the issues by manually changing Makefile when the error
occurs. 

I know little about perl internals, and thus would like to know whether it's a
easy issue to tackle. I didn't find any explicit files containing a perl.real from
perl-native sstate package, except the perl wrapper script. So it's interesting
how MakeMaker.pm finds the perl.real binary.

I reported a bug at:
http://bugzilla.yoctoproject.org/post_bug.cgi

Thanks,
Kevin