Commit 5f5fb56c68e4 ("[compiler-rt] Intercept the uname() function")
broke clang-cmake-thumbv7-full-sh build:
This also affects i386.
The reason is that intercepted uname() is called by GetKernelAreaSize()
during ASAN initialization on 32-bit platforms, but the respective
interceptor is not initialized yet at this point, leading to null
Introduce internal_uname() wrapper around uname syscall, and use it in
GetKernelAreaSize() and in FixedCVE_2016_2143().