Upgrade to regalloc2 v0.2.3 to get bugfix from bytecodealliance/regalloc2#60. (#4335)

* Upgrade to regalloc2 v0.2.3 to get bugfix from bytecodealliance/regalloc2#60.

* Update RELEASES.md.

* Update two compile tests based on slightly shifting regalloc output.

cranelift/filetests/filetests/isa/aarch64/reftypes.clif

@@ -72,20 +72,20 @@ block3(v7: r64, v8: r64):
 ;   ldr x3, 8 ; b 12 ; data TestCase { length: 1, ascii: [102, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0] } + 0
 ;   blr x3
 ;   mov x9, sp
-;   ldr x10, [sp, #8]
-;   str x10, [x9]
+;   ldr x11, [sp, #8]
+;   str x11, [x9]
 ;   and w7, w0, #1
 ;   cbz x7, label1 ; b label3
 ; block1:
 ;   b label2
 ; block2:
-;   mov x1, x10
+;   mov x1, x11
 ;   ldr x0, [sp, #16]
 ;   b label5
 ; block3:
 ;   b label4
 ; block4:
-;   mov x0, x10
+;   mov x0, x11
 ;   ldr x1, [sp, #16]
 ;   b label5
 ; block5:

cranelift/filetests/filetests/isa/s390x/reftypes.clif

@@ -74,21 +74,21 @@ block3(v7: r64, v8: r64):
 ;   bras %r1, 12 ; data %f + 0 ; lg %r5, 0(%r1)
 ;   basr %r14, %r5
 ;   la %r3, 160(%r15)
-;   lg %r4, 168(%r15)
-;   stg %r4, 0(%r3)
-;   llcr %r5, %r2
-;   chi %r5, 0
+;   lg %r5, 168(%r15)
+;   stg %r5, 0(%r3)
+;   llcr %r4, %r2
+;   chi %r4, 0
 ;   jgnlh label1 ; jg label3
 ; block1:
 ;   jg label2
 ; block2:
-;   lgr %r3, %r4
+;   lgr %r3, %r5
 ;   lg %r2, 176(%r15)
 ;   jg label5
 ; block3:
 ;   jg label4
 ; block4:
-;   lgr %r2, %r4
+;   lgr %r2, %r5
 ;   lg %r3, 176(%r15)
 ;   jg label5
 ; block5: