[regexp] implement case-insensitive unicode regexps.

test/mjsunit/mjsunit.status

Index: test/mjsunit/mjsunit.status
diff --git a/test/mjsunit/mjsunit.status b/test/mjsunit/mjsunit.status
index d5ac720b4c04f9e205ceefa9af04662b7ef3c359..8b351dc3ad7ec5d0ec5938e94b80638687e81415 100644
--- a/test/mjsunit/mjsunit.status
+++ b/test/mjsunit/mjsunit.status
@@ -289,6 +289,9 @@
 
   # TODO(titzer): SSE 4.1 required for asm-wasm test (floor).
   'wasm/asm-wasm': [SKIP],
+
+    # case-insensitive unicode regexp relies on case mapping provided by ICU.
+  'harmony/unicode-regexp-ignore-case': [PASS, ['no_i18n == True', FAIL]],
 }],  # ALWAYS
 
 ['novfp3 == True', {