Fix build issues with clang 3.4

clang 3.4 (just like gcc) implements _Unwind_GetIP - use Bionic's
implementation only if older clang versions are used.

Don't set incorrect values for WCHAR_MIN and WCHAR_MAX when using clang
in c++11 mode (c++11 has a builtin wchar_t that happens to be unsigned
in clang). Signed WCHAR_MIN and WCHAR_MAX defines in clang++ -std=c++11
cause anything using stlport to fail.

Change-Id: I46ed08b873f34e01c5e66aa8d91c71478bfcc25d
Signed-off-by: Bernhard Rosenkränzer <Bernhard.Rosenkranzer@linaro.org>

Conflicts:
	libc/include/stdint.h