support: add missing locale stubs for android L, M

The strto* family was introduced in android O (API Level 26).  However,
the support headers were adjusted to indicate that all locale aware
functions were added in L.  Provide stubs for the locale aware strto*
family until O.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@330045 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed