Change cbrt implementation to use a better performing algorithm.

Fix a few warnings along the way.

[SVN r59095]

libs/math

@@ -1 +1 @@
-Subproject commit a549a4b6d5820deea9a1de658fa97a66855be4d2
+Subproject commit 1a5044497dbfa7fca9964ff81d39c66cd1e5a52b