perl: fix rebuid failed while ${CC} changed

perl: fix rebuid failed while ${CC} changed

Reproduce steps:

1) bitbake perl
2) vim local.conf to tweak CC, just add redundant option.
...
CC_append = " ${HOST_CC_ARCH}"
...

3) bitbake perl
...
./miniperl -Ilib make_ext.pl lib/auto/Time/HiRes/HiRes.so MAKE=make LIBPERL_A=libperl.so LINKTYPE=dynamic
    Making Time::HiRes (all)my $filename=
Deleting non-Cross makefile
Running Makefile.PL in cpan/Time-HiRes
Makefile.PL: The "xdefine" exists, skipping the configure step.
("tmp/sysroots/x86_64-linux/usr/bin/perl-native/perl5.20.0.real Makefile.PL --configure" to force the configure step)
Warning: No Makefile!
make[2]: Entering directory `tmp/work/armv5te-poky-linux-gnueabi/perl/5.20.0-r1/perl-5.20.0/cpan/Time-HiRes'
make[2]: *** No rule to make target `config'.  Stop.
...

While ${CC} changed, the existance of 'xdefine' caused makefile
regeneration failed.

[YOCTO #6569]

Signed-off-by: Hongxu Jia <hongxu.jia@windriver.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>