Skip Thai character test when libthai is unavailable.

Taken from upstream bug tracker:
https://gitlab.gnome.org/GNOME/pango/merge_requests/161
https://gitlab.gnome.org/GNOME/pango/commit/b73284747ac937e31dc9191f84ed6e24284c88ee

diff --git a/tests/test-break.c b/tests/test-break.c
index 8549b678bba69360d07dce3af21d915412f20d51..47fa3009165e19a331aa04a0df4351ae2323933b 100644
--- a/tests/test-break.c
+++ b/tests/test-break.c
@@ -305,6 +305,12 @@ main (int argc, char *argv[])
       if (!strstr (name, "break"))
         continue;
 
+#ifndef HAVE_LIBTHAI
+      /* four.break involves Thai, so only test it when we have libthai */
+      if (strstr (name, "four.break"))
+        continue;
+#endif
+
       path = g_strdup_printf ("/break/%s", name);
       g_test_add_data_func_full (path, g_test_build_filename (G_TEST_DIST, "breaks", name, NULL),
                                  test_break, g_free);
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<tr><td><span title='2019-06-07 21:50:18 +0200'>2019-06-07</span></td><td><a href='/guix/commit/gnu/system/locale.scm?id=15ec93a7832ae7dde747ccd9bb2bb2776be9f199'>Add (gnu build locale).</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-05-13 23:46:08 +0200'>2019-05-13</span></td><td><a href='/guix/commit/gnu/system/locale.scm?id=1be065c4784805e7a7b4c3f08970d8e4043b0a60'>locale: Add 'glibc-supported-locales'.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2018-01-24 11:18:49 -0500'>2018-01-24</span></td><td><a href='/guix/commit/gnu/system/locale.scm?id=6d5a65de7fba53ca1160844550d261f540f110e1'>system: Put locales where libc will find them.</a><span class='msg-avail'>...</span></td><td>Mark H Weaver</td></tr>
<tr><td><span title='2017-07-17 23:41:36 +0200'>2017-07-17</span></td><td><a href='/guix/commit/gnu/system/locale.scm?id=b19a49d015070f9109c157bc39b47574a8dad481'>locale: Demonadify the locale creation API.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2017-07-17 23:41:36 +0200'>2017-07-17</span></td><td><a href='/guix/commit/gnu/system/locale.scm?id=6d833b13b77f6b4fb76acab932fd9cec601b71ac'>gnu: Remove glibc@2.21 and its traces.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2017-07-11 22:47:08 +0200'>2017-07-11</span></td><td><a href='/guix/commit/gnu/system/locale.scm?id=4ddb64f57d0e9133f8083ee5c6398fa829ed0eab'>system: Refer to native packages when appropriate.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>