[PATCH 0/3] Extend -falign-FOO=N to N[,M[,N2[,M2]]] version 4

[Denys Vlasenko <dvlasenk@redhat.com>]

These patches are for this bug:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66240
"RFE: extend -falign-xyz syntax"

The test program:

int g();
int f(int i) {
        i *= 3;
        while (--i > 100) {
 L1:            if (g()) goto L1;
                if (g()) goto L2;
        }
        return i;
 L2:    return 123;
}

"-O2" assembly before the patch:	After the patch:
        .text                           	.text
        .p2align 4,,15                  	.p2align 4
        .globl  f                       	.globl	f
        .type   f, @function            	.type	f, @function
f:                                      f:
.LFB0:                                  .LFB0:
        pushq   %rbx                    	pushq	%rbx
        leal    (%rdi,%rdi,2), %ebx     	leal	(%rdi,%rdi,2), %ebx
        .p2align 4,,10                  	.p2align 4,,10
        .p2align 3                      	.p2align 3
.L2:                                    .L2:
        subl    $1, %ebx                	subl	$1, %ebx
        cmpl    $100, %ebx              	cmpl	$100, %ebx
        jle     .L1                     	jle	.L1
        .p2align 4,,10                  	.p2align 4,,10
        .p2align 3                      	.p2align 3
.L3:                                    .L3:
        xorl    %eax, %eax              	xorl	%eax, %eax
        call    g                       	call	g
        testl   %eax, %eax              	testl	%eax, %eax
        jne     .L3                     	jne	.L3
        call    g                       	call	g
        testl   %eax, %eax              	testl	%eax, %eax
        je      .L2                     	je	.L2
        movl    $123, %ebx              	movl	$123, %ebx
.L4:                                    .L4:
.L1:                                    .L1:
        movl    %ebx, %eax              	movl	%ebx, %eax
        popq    %rbx                    	popq	%rbx
        ret                             	ret

This is version 6 of the patch set.

Bernd asked to replace use of a new SUBALIGN_LOG define with a hook.
Don't see an easy way to do that (short of adding a dedicated hook),
for now retained SUBALIGN_LOG method. Suggestions welcome.

Changes since version 5:

* Changes in rs6000, mips, alpha, visium, sh, rx, spu to accomodate
  new alignment options.
* Explicitly list secondary alignment of 8 ("n,m,8") in x86 tables
  for all types of jump targets.

Changes since version 4:

* Deleted rather than NOPed -malign-foo=N support.
* Improved behavior match with x86 8-byte subalignment for labels.

Changes since version 3:

* Improved documentation in invoke.texi
* Fixed x86-specific calculation of default N2 value:
  previous version was doing it incorrectly for cross-compile