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:
6588fa0e9de48716ff3ec6159c67c9afc'/><select name='h' onchange='this.form.submit();'>
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<tr><td class='sub'>Wojtek's customized Guix</td><td class='sub right'></td></tr></table>
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<div class='path'>path: <a href='/guix/log/?id=726b0766588fa0e9de48716ff3ec6159c67c9afc'>root</a>/<a href='/guix/log/gnu?id=726b0766588fa0e9de48716ff3ec6159c67c9afc'>gnu</a>/<a href='/guix/log/gnu/installer?id=726b0766588fa0e9de48716ff3ec6159c67c9afc'>installer</a>/<a href='/guix/log/gnu/installer/hardware.scm?id=726b0766588fa0e9de48716ff3ec6159c67c9afc'>hardware.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/installer/hardware.scm?id=726b0766588fa0e9de48716ff3ec6159c67c9afc&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2022-11-15 12:16:43 +0100'>2022-11-15</span></td><td><a href='/guix/commit/gnu/installer/hardware.scm?id=514fedbf3966b7fbab31a6c63b4210ec8b5b0c9a'>installer: Report known-unsupported PCI devices.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/installer/hardware.scm: New file.
* gnu/local.mk (INSTALLER_MODULES): Add it.
* po/guix/POTFILES.in: Add it.
* gnu/installer.scm (installer-steps): Pass #:pci-database to the
'welcome' step procedure.
* gnu/installer/newt.scm (welcome-page): Add #:pci-database and pass it
to 'run-welcome-page'.
* gnu/installer/newt/welcome.scm (check-hardware-support): Add #:pci-database.
Enumerate unsupported PCI devices and run an error page when unsupported
devices are found.
(run-welcome-page): Add #:pci-database and pass it to
'check-hardware-support' and to the recursive call.
* gnu/installer/record.scm (&lt;installer&gt;)[welcome-page]: Adjust comment.
* doc/guix.texi (Hardware Considerations): Mention it.
</span></span></td><td>Ludovic Courtès</td></tr>