Disable failing Cygwin GIR test.
diff --git a/run_unittests.py b/run_unittests.py
index 550fe36..d2e9161 100755
--- a/run_unittests.py
+++ b/run_unittests.py
@@ -3058,6 +3058,8 @@
 
     @skip_if_not_base_option('b_lto_threads')
     def test_lto_threads(self):
+        if is_cygwin():
+            raise unittest.SkipTest('LTO is broken on Cygwin.')
         testdir = os.path.join(self.common_test_dir, '6 linkshared')
 
         env = get_fake_env(testdir, self.builddir, self.prefix)
diff --git a/test cases/frameworks/11 gir subproject/meson.build b/test cases/frameworks/11 gir subproject/meson.build
index a599ae9..75cd941 100644
--- a/test cases/frameworks/11 gir subproject/meson.build
+++ b/test cases/frameworks/11 gir subproject/meson.build
@@ -5,6 +5,10 @@
   error('MESON_SKIP_TEST g-ir-scanner not found.')
 endif
 
+if build_machine.system() == 'cygwin'
+  error('MESON_SKIP_TEST GIR seems to be broken in Cygwin and no-one knows how to fix it. Thus we have to disable this.')
+endif
+
 python3 = import('python3')
 py3 = python3.find_python()
 if run_command(py3, '-c', 'import gi;').returncode() != 0
diff --git a/test cases/frameworks/12 multiple gir/meson.build b/test cases/frameworks/12 multiple gir/meson.build
index ddc9830..cf5df8c 100644
--- a/test cases/frameworks/12 multiple gir/meson.build
+++ b/test cases/frameworks/12 multiple gir/meson.build
@@ -5,6 +5,10 @@
   error('MESON_SKIP_TEST g-ir-scanner not found.')
 endif
 
+if build_machine.system() == 'cygwin'
+  error('MESON_SKIP_TEST GIR seems to be broken in Cygwin and no-one knows how to fix it. Thus we have to disable this.')
+endif
+
 gnome = import('gnome')
 gobj = dependency('gobject-2.0')
 
diff --git a/test cases/frameworks/22 gir link order/meson.build b/test cases/frameworks/22 gir link order/meson.build
index 8a714b5..36c652d 100644
--- a/test cases/frameworks/22 gir link order/meson.build
+++ b/test cases/frameworks/22 gir link order/meson.build
@@ -4,6 +4,10 @@
   error('MESON_SKIP_TEST glib not found.')
 endif
 
+if build_machine.system() == 'cygwin'
+  error('MESON_SKIP_TEST GIR seems to be broken in Cygwin and no-one knows how to fix it. Thus we have to disable this.')
+endif
+
 gnome = import('gnome')
 glib = dependency('glib-2.0')
 gobject = dependency('gobject-2.0')
diff --git a/test cases/frameworks/28 gir link order 2/meson.build b/test cases/frameworks/28 gir link order 2/meson.build
index a26531b..88aa277 100644
--- a/test cases/frameworks/28 gir link order 2/meson.build
+++ b/test cases/frameworks/28 gir link order 2/meson.build
@@ -4,6 +4,10 @@
   error('MESON_SKIP_TEST gobject not found.')
 endif
 
+if build_machine.system() == 'cygwin'
+  error('MESON_SKIP_TEST GIR seems to be broken in Cygwin and no-one knows how to fix it. Thus we have to disable this.')
+endif
+
 gnome = import('gnome')
 gobject = dependency('gobject-2.0')
 
diff --git a/test cases/vala/11 generated vapi/meson.build b/test cases/vala/11 generated vapi/meson.build
index d5f38ca..eb57649 100644
--- a/test cases/vala/11 generated vapi/meson.build
+++ b/test cases/vala/11 generated vapi/meson.build
@@ -1,5 +1,9 @@
 project('vapi-test', ['c', 'vala'])
 
+if build_machine.system() == 'cygwin'
+  error('MESON_SKIP_TEST GIR seems to be broken in Cygwin and no-one knows how to fix it. Thus we have to disable this.')
+endif
+
 gnome = import('gnome')
 subdir('libfoo')
 subdir('libbar')