Unixify path in t/INSTALL_BASE.t.

98fdebd96dd broke the test on VMS because rel2abs converts the
directory to a native path, which we then paste Unix-style path
components onto, resulting in an invalid mogrel path.

N.B.  We can't just call File::Spec::Unix->rel2abs because that
calls $self->canonpath, which, on VMS, also converts the path to
native format.
Must be in t/ to call perl_lib().

The whole purpose of MakeMaker::Test::Utils::perl_lib is to set up
$ENV{PERL5LIB} relative to the t/ directory, but since 38e7337a43b
it hasn't been doing that for some tests because they've already
navigated to a temp directory before perl_lib is called.

Test::Harness, t/TEST, and t/harness mostly compensate by doing
their own mangling of $ENV{PERL5LIB}, but if you have a failing test
and run it by itself, and if it happens to run commands in child
processes (such as "perl Makefile.PL"), you'll likely be testing
the MakeMaker from your installed Perl rather than the one in the
MakeMaker distribution.

So modify those tests that chdir to a temp directory to call
perl_lib first before navigating below t/.
Delete unused PM_TO_BLIB macro
Space-quote pm_to_blib args
Absolutise all typemaps because with deep-located typemaps, eg
"lib/XS/typemap", if xsubpp is called from top level with
    $(XSUBPP) ... -typemap "lib/XS/typemap" "lib/XS/Test.xs"
it says:
    Can't find lib/XS/type map in (fulldir)/lib/XS
because ExtUtils::ParseXS::process_file chdir's to .xs file's
location. This is the only way to get all specified typemaps used,
wherever located.
xs_obj_opt method adds -o to all $(CCCMD) commands to put .o next to .c
Eliminate && from Makefile recipes - totally unnecessary
Sort realclean files = diff-able Makefiles
RE with interpolated filename needs quotemeta
Make t/xs.t et al pluggable
Refactor dynamic_lib
Refactor dlsyms
Refactor dynamic_bs
Refactor xs_o and xs_c
Enable XSMULTI: multi *.xs under lib/ "just work"
Test, fix static build XS
t/xs.t even more pluggable with extra args to make calls
Break pure_all target into pure_nolink and linkext.
This allows breaking subdirs into subdirs_static and subdirs_dynamic.
This in turn allows building either static or dynamic when subdirs.
Add t/xs.t subdirsstatic to test.
Test, fix static XSMULTI
Minor tidyup in makeaperl