devtools: add test script for meson builds

devtools: add test script for meson builds

To simplify testing with the meson and ninja builds, we can add a script
to set up and do multiple builds. Currently this script sets up:

* clang and gcc builds
* builds using static and shared linkage for binaries (libs are always
   built as both)
* a build using the lowest instruction-set level for x86 (-march=nehalem)
* cross-builds for each cross-file listed in config/arm

Each build is configured in a directory ending in *-build, and then for
the build stage, we just call ninja in each directory in turn. [i.e. we
assume every directory starting with "build-" is a meson build, which is
probably an ok assumption].

Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
Signed-off-by: Thomas Monjalon <thomas@monjalon.net>