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:
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<div class='path'>path: <a href='/guix/log/?id=5c26e06efa38f82957154a3f0e29c27e04615542'>root</a>/<a href='/guix/log/gnu?id=5c26e06efa38f82957154a3f0e29c27e04615542'>gnu</a>/<a href='/guix/log/gnu/packages?id=5c26e06efa38f82957154a3f0e29c27e04615542'>packages</a>/<a href='/guix/log/gnu/packages/mp3.scm?id=5c26e06efa38f82957154a3f0e29c27e04615542'>mp3.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/mp3.scm?id=5c26e06efa38f82957154a3f0e29c27e04615542&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2023-02-19 01:00:18 +0100'>2023-02-19</span></td><td><a href='/guix/commit/gnu/packages/mp3.scm?id=a52074001ffe01d6d864f0b70d624b6a0a64bba7'>gnu: mpg123: Update to 1.31.2.</a></td><td>Vasile Dumitrascu via Guix-patches via</td></tr>
<tr><td><span title='2023-02-19 01:00:01 +0100'>2023-02-19</span></td><td><a href='/guix/commit/gnu/packages/mp3.scm?id=1e6ddceb8318d413745ca1c9d91fde01b1e0364b'>gnu: Use HTTPS package home pages wherever possible.</a></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2022-12-12 15:12:58 +0100'>2022-12-12</span></td><td><a href='/guix/commit/gnu/packages/mp3.scm?id=79564bf9977ebba0b31d8dc291eb039142f51f68'>gnu: ffmpeg: Promote version 5 to the default.</a></td><td>Marius Bakke</td></tr>
<tr><td><span title='2022-08-06 23:14:41 +0200'>2022-08-06</span></td><td><a href='/guix/commit/gnu/packages/mp3.scm?id=902fea913682d5ae878a26f1522536a289695631'>gnu: Add wavbreaker.</a></td><td>Joeke de Graaf</td></tr>
<tr><td><span title='2022-08-03 13:59:37 +0800'>2022-08-03</span></td><td><a href='/guix/commit/gnu/packages/mp3.scm?id=cb14d802aef0aaa475147e0a5cc36ff71e631a62'>gnu: Add minimp3.</a></td><td>John Kehayias</td></tr>
<tr><td><span title='2022-04-04 19:57:12 -0400'>2022-04-04</span></td><td><a href='/guix/commit/gnu/packages/mp3.scm?id=20303c0b1c75bc4770cdfa8b8c6b33fd6e77c168'>gnu: eyeD3: Update to 0.9.6.</a></td><td>Leo Famulari</td></tr>
<tr><td><span title='2022-01-16 01:00:00 +0100'>2022-01-16</span></td><td><a href='/guix/commit/gnu/packages/mp3.scm?id=06bf24dcb9843c1885f892624b8a19046b9d2ca2'>gnu: chromaprint: Update to 1.5.1.</a></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2021-12-13 17:48:25 +0100'>2021-12-13</span></td><td><a href='/guix/commit/gnu/packages/mp3.scm?id=8394619baceb118df92e355377fd543bb1aa501a'>gnu: Simplify package inputs.</a></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2021-09-18 15:31:18 +0200'>2021-09-18</span></td><td><a href='/guix/commit/gnu/packages/mp3.scm?id=19c9c266ae1de85e9d731e3ad829c8273b641c83'>gnu: mpg321: Fix compiling with gcc 10.</a></td><td>Guillaume Le Vaillant</td></tr>
<tr><td><span title='2021-09-11 18:14:06 +0200'>2021-09-11</span></td><td><a href='/guix/commit/gnu/packages/mp3.scm?id=83168079ac176563ed2b448bb1b2fd0e5d4a5dc3'>gnu: mpc123: Allow compilation with GCC 10.</a></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2021-09-07 14:19:08 +0200'>2021-09-07</span></td><td><a href='/guix/commit/gnu/packages/mp3.scm?id=d9dfbf886ddbb92dfdaa118bb9765e78aad5c53a'>Merge branch 'master' into core-updates-frozen</a></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2021-09-04 14:53:34 +0200'>2021-09-04</span></td><td><a href='/guix/commit/gnu/packages/mp3.scm?id=9f543674ff0f2f178b656597fef24e834635d60b'>gnu: python-pyacoustid: Update to 1.2.2.</a></td><td>Lars-Dominik Braun</td></tr>
<tr><td><span title='2021-08-12 00:30:27 +0200'>2021-08-12</span></td><td><a href='/guix/commit/gnu/packages/mp3.scm?id=c4133c43c7cfe2476ebfae87f9e4d10d96de9bc7'>Merge branch 'master' into core-updates-frozen</a></td><td>Marius Bakke</td></tr>
<tr><td><span title='2021-08-04 16:34:31 +0300'>2021-08-04</span></td><td><a href='/guix/commit/gnu/packages/mp3.scm?id=bc38598c8eb8b7df125c16a38ae4c1180e1f6979'>gnu: mpg123: Update to 1.28.2.</a></td><td>Efraim Flashner</td></tr>
<tr><td><span title='2021-07-25 17:52:36 +0200'>2021-07-25</span></td><td><a href='/guix/commit/gnu/packages/mp3.scm?id=a682fea916b9f3ff101a76273aa754e11d53244d'>gnu: gs-font: Rename to 'font-ghostscript'.</a></td><td>Maxime Devos</td></tr>