Make: fix installation instructions

ARM: do not add linker flag `-lm` unconditionally

ARM: recognize gfortran pre-releases

The installation instructions as shown after successfully compiling
OpenBLAS are wrong because this arguments used during compilation have
to be provided to Make again.

On ARM the required math library depends on whether the soft floating
point ABI is used or not but this is already handled in
`Makefile.system`, lines 499-505.

Without proper recognition of gfortran versions such as
> GNU Fortran (GCC) 4.9.x 20150123 (prerelease)
OpenBLAS assumes the presence of the G77 compiler. Consequently,
`-lgfortran` is missing from the pkg-config file.

The aforementioned compiler is the gfortran compiler in the Android repo
in a commit tagged as `ndk-r14`, cf. Paul Mustière's gfortran build
instructions for Android at https://github.com/buffer51/android-gfortran

Support DYNAMIC_ARCH with CMake

Travis: Add jobs building with clang and disable job `LINUX64_MUSL USE_OPENMP=1`

,,,to see if this has any influence on the recent ld SIGKILLS

Make sure that range limit of last thread never exceeds data size

Support compiling with clang on windows

https://github.com/xianyi/OpenBLAS/pull/1255#issuecomment-320494610

THUDNERX2T99: Fix clang compilation

CMake Improvements

TODO: Fix the parser macro to strip trailing whitespaces

Travis: Rewrite config, build and test also on Alpine Linux (musl libc)

See: https://github.com/xianyi/OpenBLAS/pull/1255#issuecomment-318692183

See: https://github.com/xianyi/OpenBLAS/pull/1255#issuecomment-318628666

Alpine jobs needs sudo (for chroot), so they run on VMs infrastructure.
That's why they are much slower than other jobs.

Using APT addon has nice side-effect - you don't need sudo anymore, so
it can run on Travis containers-based infrastructure that is much faster
than their VMs infrastructure (used when sudo is needed).

You've been still running on Ubuntu Presty builders, but new default is
Trusty. Thus I've explicitly set `dist: presty` to let it stay on
Presty, to not change build environment by this commit.

Revert "Fix calculated range limit exceeding actual data size for last thread"

Rework __GLIBC_PREREQ checks to avoid breaking non-glibc builds