Remove non-include paths from INC in pre-build checks

While trying to get `PDL::Graphics::PLplot` to install, I found it kept
telling me that it needed a plplot library compiled with the
`--with-double` option:

```
$ perl Makefile.PL
Use of uninitialized value $size in numeric eq (==) at Makefile.PL line 46.
Sizeof(PLFLT) must be 8.
PLplot must be compiled --with-double (IE ./configure --with-double).

Please either:
- Install PLplot using your package manager then reinstall Alien::PLplot
  or
- Reinstall Alien::PLplot from CPAN with environment variable
  ALIEN_INSTALL_TYPE=share.
```

After having tried the advice about reinstalling `Alien::PLplot` and
failing, and having checked that `libplplot` had been installed using
double precision, I happened to stumble upon the issue that the option
`-pthread` was appearing in the `$plplot_include_path` variable.  I
noticed this by replacing the call to `check_lib` (from
`Devel::CheckLib`) with `check_lib_or_exit`.  When using this function,
the error output was this instead:

```
$ perl Makefile.PL
INC argument badly-formed: -pthread
```

Upon reading the docs for `Devel::CheckLib`, it turns out that the `INC`
option to both `check_lib` and `check_lib_or_exit` needs to be a
space-delimited list of options, all of which start with `-I`.  Since
`-pthread` doesn't start with `-I` the argument was badly formed, hence
the `analyze_binary` callback was never called.  Thus no check code was
compiled which then resulted in `$size` being set to `undef`.  Because
`$size` was `undef`, the uninitialized value warning mentioned in the
first error message mentione above and the check for a double precision
library failed.  In other words, because `-pthread` was turning up in
the `$plplot_include_path` string, the test for a library compiled with
the `--with-double` option was failing and hence `PDL::Graphics::PLplot`
failed to install.

By filtering only for include paths from the list of options originally
found in `$plplot_include_path` (i.e. selecting only options starting
with `-I` and hence excluding in this particular instance the `-pthread`
option), one avoids the issue of a badly formed INC argument and thus
the checks in `Makefile.PL` compile and run.  Because all checks run,
the `Makefile` is created as per normal and the test suite passes.

More background info: I found this issue on Debian version 11.11 with a
perlbrewed perl, version 5.32.1.

Author: paultcochrane

Makefile.PL

@@ -4,6 +4,7 @@ use ExtUtils::MakeMaker;
 use Config;
 use File::Spec;
 use Data::Dumper;
+use Text::ParseWords qw(shellwords);
 
 use PDL::Core::Dev;
 use Devel::CheckLib;
@@ -113,10 +114,14 @@ sub compileAndRun {
   my ($code) = @_;
   my $result;
 
+  my @inc = shellwords($plplot_include_path);
+  @inc = grep {/^-I/ } @inc;
+  my $inc = join " ", @inc;
+
   check_lib(
     ccflags  => "$plplot_include_path",
     ldflags  => "$libs",
-    INC      => "$plplot_include_path",
+    INC      => "$inc",
     LIBS     => "$libs",
     header   => [ 'stdio.h', $header ],
     function => $code,