Make sure the build system honors CPATH and LIBRARY_PATH when
looking for headers and libraries.

--- a/setup.py	2015-10-07 23:32:58.891329173 +0200
+++ b/setup.py	2015-10-07 23:46:29.653349924 +0200
@@ -575,8 +575,8 @@
         # if a file is found in one of those directories, it can
         # be assumed that no additional -I,-L directives are needed.
         if not cross_compiling:
-            lib_dirs = self.compiler.library_dirs + system_lib_dirs
-            inc_dirs = self.compiler.include_dirs + system_include_dirs
+            lib_dirs = os.getenv('LIBRARY_PATH', '').split(os.pathsep)
+            inc_dirs = os.getenv('CPATH', '').split(os.pathsep)
         else:
             # Add the sysroot paths. 'sysroot' is a compiler option used to
             # set the logical path of the standard system headers and
scripts</option>
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<div class='path'>path: <a href='/guix/log/?id=f6974e15cfce8128d9a3fb425671b1f6fc05e49b'>root</a>/<a href='/guix/log/gnu?id=f6974e15cfce8128d9a3fb425671b1f6fc05e49b'>gnu</a>/<a href='/guix/log/gnu/packages?id=f6974e15cfce8128d9a3fb425671b1f6fc05e49b'>packages</a>/<a href='/guix/log/gnu/packages/license.scm?id=f6974e15cfce8128d9a3fb425671b1f6fc05e49b'>license.scm</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/gnu/packages/license.scm?id=f6974e15cfce8128d9a3fb425671b1f6fc05e49b&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2018-10-04 06:28:26 +0200'>2018-10-04</span></td><td><a href='/guix/commit/gnu/packages/license.scm?id=104f475f9b95953a67640a82127ade689931a6e7'>gnu: perl-string-copyright: Update to 0.003006.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/license.scm (perl-string-copyright): Update to 0.003006.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2018-08-15 20:58:07 +0300'>2018-08-15</span></td><td><a href='/guix/commit/gnu/packages/license.scm?id=44d085b4c6d2ac28d6d43303b108e2812151bf2b'>gnu: licensecheck: Update to 3.0.36.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/license.scm (licensecheck): Update to 3.0.36.
(perl-regexp-pattern-license): Update to 3.1.92.
</span></span></td><td>Oleg Pykhalov</td></tr>
<tr><td><span title='2018-08-11 17:22:31 +0200'>2018-08-11</span></td><td><a href='/guix/commit/gnu/packages/license.scm?id=9aba9b127840a116c806a2cbac901cf8077abcd0'>Migrate search.cpan.org home pages to metacpan.org.</a><span class='msg-avail'>...<span class='msg-tooltip'>The venerable search.cpan.org has retired[0].

[0]: https://log.perl.org/2018/05/goodbye-search-dot-cpan-dot-org.html

* guix/import/cpan.scm (cpan-home): Generate metacpan.org home page URIs.
Update all previously generated ones in (gnu packages) to their
canonical new homes.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2018-04-05 06:39:01 +0200'>2018-04-05</span></td><td><a href='/guix/commit/gnu/packages/license.scm?id=7b3a95e5d401fb7bb9b8a3e9155f04b5fbedbdaa'>gnu: licensecheck: Update to 3.0.34.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/license.scm (licensecheck): Update to 3.0.34.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2018-02-24 20:01:31 +0300'>2018-02-24</span></td><td><a href='/guix/commit/gnu/packages/license.scm?id=f09cb93e3a2310f7726cb98fa5679c1a8483c39f'>gnu: Add licensecheck.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/license.scm (licensecheck): New public variable.
</span></span></td><td>Oleg Pykhalov</td></tr>
<tr><td><span title='2018-02-24 20:01:30 +0300'>2018-02-24</span></td><td><a href='/guix/commit/gnu/packages/license.scm?id=82e5e0dd52aac659a57bf07ae55e86cd531ea099'>gnu: Add perl-software-license.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/license.scm (perl-software-license): New public variable.
</span></span></td><td>Oleg Pykhalov</td></tr>
<tr><td><span title='2018-02-24 20:01:29 +0300'>2018-02-24</span></td><td><a href='/guix/commit/gnu/packages/license.scm?id=f4e2d9ee6cf49ae7a9ff9a084517c274ea791955'>gnu: Add perl-string-copyright.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/license.scm (perl-string-copyright): New public variable.
</span></span></td><td>Oleg Pykhalov</td></tr>
<tr><td><span title='2018-02-24 20:01:29 +0300'>2018-02-24</span></td><td><a href='/guix/commit/gnu/packages/license.scm?id=d5ee4342c0e62124a6efeb7da4c53c1f69c51d1e'>gnu: Add perl-regexp-pattern-license.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/license.scm: New file.
* gnu/local.mk (GNU_SYSTEM_MODULES): Add this.
</span></span></td><td>Oleg Pykhalov</td></tr>