Use -nostdlib++ instead of -nodefaultlibs

Host builds using libc++ used -nodefaultlibs to turn off the default
C++ runtime, and then added back all the other necessary libraries.
Clang supports -nostdlib++ since https://reviews.llvm.org/D47115
that removes the C++ runtime without affecting the other default
libraries.  Use -nostdlib++, and remove the lists of default
libraries.

Test: m checkbuild
Change-Id: I722bd6596a1f3f5819f2767c29c0fa1e8b3ec0e8