HAVE_AVX2, HAVE_SSE3 and HAVE_SSE4_1 were never defined if CPU
architecture doesn't match the (86*|x86_64*|amd64*) condition.
Change-Id: If0c3128f9768f95c1f5f955db242e71c81384c6c
This change adds a check whether compiler supports some SIMD
(Single Instruction, Multiple Data) instructions. It is enabled
by default, and can be disabled by configure option --disable-simd.
The check macro is based on the AX_EXT from autoconf-archive:
www.gnu.org/software/autoconf-archive/ax_ext.html
And depends on the ax_check_compile_flag macro:
www.gnu.org/software/autoconf-archive/ax_check_compile_flag.html
Currently only the following SIMD extensions are being checked:
AVX2, SSE3, SSE4.1, but adding others is also possible. All found
extensions are being defined in the 'config.h' header.
Change-Id: Idf8fff984bd936a75c7c307338df88ba4b005817
Even when removing AC_CONFIG_MACRO_DIR aclocal insisted that it
needs to have a m4 directory. Make it happy by providing one. As git
is not tracking directories I needed to add a dummy file.