Use gcc as the default C compiler if CC is not set.

diff -ru gobject-introspection-1.58.1.orig/giscanner/__init__.py gobject-introspection-1.58.1/giscanner/__init__.py
--- gobject-introspection-1.58.1.orig/giscanner/__init__.py	1970-01-01 01:00:00.000000000 +0100
+++ gobject-introspection-1.58.1/giscanner/__init__.py	2018-12-03 13:33:28.788971299 +0100
@@ -22,6 +22,8 @@
 builddir = os.environ.get('UNINSTALLED_INTROSPECTION_BUILDDIR')
 if builddir is not None:
     __path__.append(os.path.join(builddir, 'giscanner'))
+if not 'CC' in os.environ:
+    os.environ['CC'] = 'gcc'
 try:
     from ._version import __version__
 except ImportError:
ffd2a1c01b04f631ac40186'/><select name='h' onchange='this.form.submit();'>
<option value='koszko' selected='selected'>koszko</option>
<option value='koszko-scripts'>koszko-scripts</option>
</select> <input type='submit' value='switch'/></form></td></tr>
<tr><td class='sub'>Wojtek's customized Guix</td><td class='sub right'></td></tr></table>
<table class='tabs'><tr><td>
<a href='/guix/about/'>about</a><a href='/guix/'>summary</a><a href='/guix/refs/?id=6d4d3d89486f1be1fffd2a1c01b04f631ac40186'>refs</a><a class='active' href='/guix/log/gnu/packages/simh.scm'>log</a><a href='/guix/tree/gnu/packages/simh.scm?id=6d4d3d89486f1be1fffd2a1c01b04f631ac40186'>tree</a><a href='/guix/commit/gnu/packages/simh.scm?id=6d4d3d89486f1be1fffd2a1c01b04f631ac40186'>commit</a><a href='/guix/diff/gnu/packages/simh.scm?id=6d4d3d89486f1be1fffd2a1c01b04f631ac40186'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/gnu/packages/simh.scm'>
<input type='hidden' name='id' value='6d4d3d89486f1be1fffd2a1c01b04f631ac40186'/><select name='qt'>
<option value='grep'>log msg</option>
<option value='author'>author</option>
<option value='committer'>committer</option>
<option value='range'>range</option>
</select>
<input class='txt' type='search' size='10' name='q' value=''/>
<input type='submit' value='search'/>
</form>
</td></tr></table>
<div class='path'>path: <a href='/guix/log/?id=6d4d3d89486f1be1fffd2a1c01b04f631ac40186'>root</a>/<a href='/guix/log/gnu?id=6d4d3d89486f1be1fffd2a1c01b04f631ac40186'>gnu</a>/<a href='/guix/log/gnu/packages?id=6d4d3d89486f1be1fffd2a1c01b04f631ac40186'>packages</a>/<a href='/guix/log/gnu/packages/simh.scm?id=6d4d3d89486f1be1fffd2a1c01b04f631ac40186'>simh.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/simh.scm?id=6d4d3d89486f1be1fffd2a1c01b04f631ac40186&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>