extensions: add sse2_cflags to CIE

Fixes #42
2 jobs for wip/schumaml/fix-CIE-build in 2 minutes and 13 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #384561
latest-meson-lcms

00:02:13

passed #384562
latest-meson-nolcms

00:02:05