https://gitlab.com/mbunkus/mkvtoolnix/-/commit/ba6db89e24aa84316372d59e6bba4ac88145b32a
https://bugs.gentoo.org/786978#c10
diff --git a/Rakefile b/Rakefile
index 8c9487436ac627cc503e5f233d3f9c756f67fd86..ce564127eeb136b1c1784568ad68a4d593d0931a 100644
--- a/Rakefile
+++ b/Rakefile
@@ -355,7 +355,7 @@ cxx_compiler = lambda do |*args|
     # Even -O1 causes compilation time & memory usage to skyrocket,
     # possibly exponentially, with the number of entries to
     # emplace_back() into the vector.
-    flags.gsub!(%r{ -O\d+ }, ' -O0 ')
+    flags.gsub!(%r{(^| )-O[^ ]*}, ' -O0')
   end
 
   args = [