Use 'pkg-config' instead of heuristics to find 'tk' flags.

--- matplotlib-1.4.3/setupext.py.orig	2015-12-01 14:21:19.554417453 +0100
+++ matplotlib-1.4.3/setupext.py	2015-12-02 10:39:47.282363530 +0100
@@ -1457,7 +1457,7 @@
             p = subprocess.Popen(
                 '. %s ; eval echo ${%s}' % (file, varname),
                 shell=True,
-                executable="/bin/sh",
+                executable="sh",
                 stdout=subprocess.PIPE)
             result = p.communicate()[0]
             return result.decode('ascii')
@@ -1601,8 +1601,19 @@
             #      of distros.
 
             # Query Tcl/Tk system for library paths and version string
+            def getoutput(s):
+                ret = os.popen(s).read().strip()
+                return ret
             try:
-                tcl_lib_dir, tk_lib_dir, tk_ver = self.query_tcltk()
+                pkg_config_libs = getoutput('pkg-config --libs-only-L tk').split()
+                # drop '-L' part of strings
+                pkg_config_libs = [s[2:] for s in pkg_config_libs]
+                pkg_config_ver = getoutput('pkg-config --modversion tk')
+                tk_ver = re.match(r"(\d+.\d+)[\d.]*", pkg_config_ver).group(1)
+                tcl_lib_dir = next(s for s in pkg_config_libs
+                                   if re.match(r".*-tcl-.*", s)) + '/tcl' + tk_ver
+                tk_lib_dir = next(s for s in pkg_config_libs
+                                  if re.match(r".*-tk-.*", s)) + '/tk' + tk_ver
             except:
                 tk_ver = ''
                 result = self.hardcoded_tcl_config()
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<div class='path'>path: <a href='/guix/log/?id=630c8a8d6534b678bdee459a671a840725810b17'>root</a>/<a href='/guix/log/gnu?id=630c8a8d6534b678bdee459a671a840725810b17'>gnu</a>/<a href='/guix/log/gnu/packages?id=630c8a8d6534b678bdee459a671a840725810b17'>packages</a>/<a href='/guix/log/gnu/packages/image-viewers.scm?id=630c8a8d6534b678bdee459a671a840725810b17'>image-viewers.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/image-viewers.scm?id=630c8a8d6534b678bdee459a671a840725810b17&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2021-01-24 23:58:29 +0200'>2021-01-24</span></td><td><a href='/guix/commit/gnu/packages/image-viewers.scm?id=e330a31f7b7fd1542ce413e962ee36bef9fbc586'>gnu: catimg: Update to 2.7.0.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/image-viewers.scm (catimg): Update to 2.7.0.
</span></span></td><td>Efraim Flashner</td></tr>
rotli): Update to 1.0.9.
</span></span></td><td>Marius Bakke</td></tr>