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

diff --git a/giscanner/__init__.py b/giscanner/__init__.py
index 7c2f365a..607fe341 100644
--- a/giscanner/__init__.py
+++ b/giscanner/__init__.py
@@ -21,6 +21,8 @@ import os
 builddir = os.environ.get('UNINSTALLED_INTROSPECTION_BUILDDIR')
 if builddir is not None:
     __path__.append(os.path.join(builddir, 'giscanner'))  # type: ignore  # mypy issue #1422
+if not 'CC' in os.environ:
+    os.environ['CC'] = 'gcc'
 try:
     from ._version import __version__
 except ImportError:
ss='main'><a href='/'>index</a> : <a href='/guix/'>guix</a></td><td class='form'><form method='get'>
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<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>
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<option value='grep'>log msg</option>
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<input class='txt' type='search' size='10' name='q' value=''/>
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<div class='path'>path: <a href='/guix/log/?id=7c8ee30ca691c4fdf57f0868fe56e2eaefe878f8'>root</a>/<a href='/guix/log/gnu?id=7c8ee30ca691c4fdf57f0868fe56e2eaefe878f8'>gnu</a>/<a href='/guix/log/gnu/system?id=7c8ee30ca691c4fdf57f0868fe56e2eaefe878f8'>system</a>/<a href='/guix/log/gnu/system/images?id=7c8ee30ca691c4fdf57f0868fe56e2eaefe878f8'>images</a>/<a href='/guix/log/gnu/system/images/orangepi-r1-plus-lts-rk3328.scm?id=7c8ee30ca691c4fdf57f0868fe56e2eaefe878f8'>orangepi-r1-plus-lts-rk3328.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/system/images/orangepi-r1-plus-lts-rk3328.scm?id=7c8ee30ca691c4fdf57f0868fe56e2eaefe878f8&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2023-12-22 16:06:15 -0800'>2023-12-22</span></td><td><a href='/guix/commit/gnu/system/images/orangepi-r1-plus-lts-rk3328.scm?id=ab1ff7ca40b0a2d935f715dcf64f0f3128632d3d'>images: Add orangepi-r1-plus-lts image.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/local.mk: Register image.
* gnu/system/images/orangepi-r1-plus-lts-rk3328.scm: New file.
* gnu/system/install.scm (orangepi-r1-plus-lts-rk3328-installation-os):
  New variable.

Signed-off-by: Vagrant Cascadian &lt;vagrant@debian.org&gt;
</span></span></td><td>Herman Rimm</td></tr>