Using a custom include and libs path for zlib

[vrkosk]

I'm using a bare bones sysroot (same as in issue #217 in fact) that doesn't have zlib installed. I have compiled and installed zlib in a different path, say $XYZZY, so I'd like to set a custom include path $XYZZY/include and custom linker flag -L$XYZZY/lib.

Makefile.PL has my $INCLUDE; variable, which is passed to WriteMakeFile(), but the variable is always undef. Solution is:

 push @h_dirs, qw(/include /usr/include /usr/local/include /usr/include/mach);
 @h_dirs = grep { -d $_ } @h_dirs;

+$INCLUDE = join(' ', map { sprintf('-I%s', $_) } split /:/, $ENV{INCLUDE}) if $ENV{INCLUDE};

Then configure as:

INCLUDE=$XYZZY/include perl Makefile.PL

However, there's no mechanism to set a custom library path. Essentially, I want to push something to @libs before it's passed to WriteMakeFile().