Merge from develop for 0.3.12 release

Comment out  BUILD_SINGLE etc. in Makefile.rule and add a short explanation

Fix grouping of sladiv1/dladiv1/ilaenv2stage in gensymbol

rebase

Increase and unify BUFFERSIZE on POWER;fix gcc inline warning

Fix twisted spelling that broke the gfortran version test again

Fix compiler version check for -mavx2 support (DYNAMIC_ARCH case)

Fix macro used in argument conversion (LAPACK PR 458)

to fix overflow warning for PWR8 ZGEMM and PWR9 C/ZGEMM and avoid size mismatches in DYNAMIC_ARCH

rebase

Optimize scopy/ccopy for POWER10

actually check that version is greater than 4.7

This patch makes use of new POWER10 vector pair instructions for
loads and stores. Also reorganized all variants of copy functions
to make use of same kernel.

Fix build with -Werror=return-type

Enable -mavx2 for flang as well where supported

dgemm_tcopy_16_skylakex.c CNAME function should return an int, add a
return 0 similar to other files.

rebase

Add binutils version check as prerequisite for POWER10 in DYNAMIC_ARCH build

x86_64: clobber all xmm registers after vzeroupper

As observed using GCC 10 using -march=native -ftree-vectorize
on Knights Landing, it is now smart enough to find clobbers inside
non-inlined static functions.

In particular, sgemv counted on a kernel to preserve the whole
%ymm2 register (since it was not in the clobber list), but the top
part was destroyed by vzeroupper. This caused many tests to fail.

This patch makes sure all xmm (and ymm/zmm by extension) registers
are listed as clobbered to avoid this happening, as most kernels
already did correctly in fact.

to be able to include a binutils version check

rebase

Put back all symbols accidentally dropped in the reorganization of gensymbol

Clean up duplicate definitions in POWER8 kernels and fix power10 option passing

rebase

Fix exporting some lapack and cblas symbols

sgemm_direct_skylakex: fix 75eeb26 regression.

Support cross-compiling for Apple Vortex