[sanitizer] increase the minimal mmap size in allocator to 2^16; fix the asan Mac build 

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@173261 91177308-0d34-0410-b5e6-96231b3b80d8
[msan] Allow waitpid while in __msan_init().

This is used in symbolizer init.


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@173263 91177308-0d34-0410-b5e6-96231b3b80d8