[gtksourceview/gtksourceview-5-4] c.lang: highlight C99 Unicode escapes

[Christian Hergert <chergert src gnome org>]

commit bf6046eeec04c418bf882f39488818a3f9bc8eff
Author: Elias Aebi <353-eyelash users noreply gitlab gnome org>
Date:   Wed Apr 27 10:07:22 2022 +0200

    c.lang: highlight C99 Unicode escapes

 data/language-specs/c.lang | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)
---
diff --git a/data/language-specs/c.lang b/data/language-specs/c.lang
index 48c7f9c4..c54b1bfa 100644
--- a/data/language-specs/c.lang
+++ b/data/language-specs/c.lang
@@ -62,7 +62,9 @@
       \\(                   # leading backslash
       [\\\"\'nrbtfav\?] |   # escaped character
       [0-7]{1,3} |          # one, two, or three octal digits
-      x[0-9A-Fa-f]+         # 'x' followed by hex digits
+      x[0-9A-Fa-f]+ |       # 'x' followed by hex digits
+      u[0-9A-Fa-f]{4} |     # 'u' followed by 4 hex digits
+      U[0-9A-Fa-f]{8}       # 'U' followed by 8 hex digits
       )
     </define-regex>