Power8 inline assembly tweaks

Further fixes on top of 9e2f316ed.  Writing some doco for gcc on
inline assembly woke me up to some more errors.

- dgemv_kernel_4x4 asm did not mention *ap as a memory input, and
  *y is both read and write.
- sasum_kernel_32 and casum_kernel_16 did not use %x for a vsx insn
  operand, a problem if the "=f" sum output was ever allocated a vsx
  reg in the altivec set.  This might be possible with inlining and
  future gcc optimisation.

Autodetect AMD A8-6410 as BARCELONA

* Fix integer overflow in DBDSQR

As noted in lapack issue 135, an integer overflow in the calculation of the iteration limit could lead to an immediate return without any iterations having been performed if the input matrix is sufficiently big.

* Fix integer overflow in SBDSQR

As noted in lapack issue 135, an integer overflow in the calculation of the iteration limit could lead to an immediate return without any iterations having been performed if the input matrix is sufficiently big.

* Fix integer overflow in threshold calculation

Related to lapack issue 135, the threshold calculation can overflow as well as the multiplication is evaluated from left to right.
Without explicit parentheses, the calculation would overflow for N >= 18919

* Fix integer overflow in threshold calculation

Related to lapack issue 135, the threshold calculation can overflow as well as the multiplication is evaluated from left to right.
Without explicit parentheses, the calculation would overflow for N >= 18919

Add ZEN support

* fix unlikely memleak in zimatcopy interface

* fix only unlikely memleak in zimatcopy interface

* fix only unlikely memleak in zimatcopy interface

Blas 3 for single precision

Fix compilation with PGI by replacing verbatim _real_, _imag_ extensions and updating macro definitions for modern, C99-capable versions of the PGI compiler

Update c_check.cmake to label ppc64 as power ARCH

Fix misspelling of zlasyf_aa from previous commit

Add `csymv` and `zsymv` into `@lapackobjs2` for exporting

Fix core detection for Kaby Lake without AVX (G4560)

Should fix #1109)

Conventional usage of the register save area.

Optimized Implementations for ThunderX2T99

ztrmm(zgemm) complex double precision kernel for ibm z13

remove input from clobbered list

TESTING/EIG: fix spurious EXTERNAL references to nonexistent functions

Remove unused (and nonexistent) functions ZHETRD_SY2SB and ZHETRD_SB2ST from comment and EXTERNAL declaration

Remove unused (and nonexistent) ZHETRD_SY2SB and ZHETRD_SB2ST

ZHBTRD_HB2ST  should be ZHETRD_HB2ST

LAPACK: fix missing comma on continued lines

EXTERNAL declaration of subroutines missed a comma before the continuation line,
causing a strange run-together name to appear in the object when compiled with ifort.

EXTERNAL declaration of subroutines missed a comma before the continuation line,
causing a strange run-together name to appear in the object when compiled with ifort.

EXTERNAL declaration of subroutines missed a comma before the continuation line,
causing a strange run-together name to appear in the object when compiled with ifort.

EXTERNAL declaration of subroutines missed a comma before the continuation line,
causing a strange run-together name to appear in the object when compiled with ifort.

LAPACKE: fix wrong matrix size in ?ormbr