Don't renumber entities in the parser.

This makes it easier to debug testcases:
 - the entity numbers in a .cton file match the entity numbers used
   within Cretonne.
 - serializing and deserializing doesn't cause indices to change.

One disadvantage is that if a .cton file uses sparse entity numbers,
deserializing to the in-memory form doesn't compact it. However, the
text format is not intended to be performance-critical, so this isn't
expected to be a big burden.

cranelift/filetests/isa/intel/allones_funcaddrs32.cton

@@ -11,8 +11,8 @@ isa intel haswell
 
 ; Tests from binary32.cton affected by allones_funcaddrs.
 function %I32() {
-    fn0 = function %foo()
     sig0 = ()
+    fn0 = function %foo()
 
 ebb0:
 

cranelift/filetests/isa/intel/allones_funcaddrs64.cton

@@ -12,8 +12,8 @@ isa intel haswell
 
 ; Tests from binary64.cton affected by allones_funcaddrs.
 function %I64() {
-    fn0 = function %foo()
     sig0 = ()
+    fn0 = function %foo()
 
 ebb0:
 

cranelift/filetests/isa/intel/binary32.cton

@@ -9,8 +9,8 @@ isa intel haswell
 ;
 
 function %I32() {
-    fn0 = function %foo()
     sig0 = ()
+    fn0 = function %foo()
 
     gv0 = globalsym %some_gv
 

cranelift/filetests/isa/intel/binary64-pic.cton

@@ -12,8 +12,8 @@ isa intel haswell
 
 ; Tests for i64 instructions.
 function %I64() {
-    fn0 = function %foo()
     sig0 = ()
+    fn0 = function %foo()
 
     gv0 = globalsym %some_gv
 

cranelift/filetests/isa/intel/binary64.cton

@@ -11,8 +11,8 @@ isa intel haswell
 
 ; Tests for i64 instructions.
 function %I64() {
-    fn0 = function %foo()
     sig0 = ()
+    fn0 = function %foo()
 
     gv0 = globalsym %some_gv
 
@@ -641,8 +641,8 @@ ebb1:
 ; encodings which are chosen by default. Switching to non-REX encodings should
 ; be done by an instruction shrinking pass.
 function %I32() {
-    fn0 = function %foo()
     sig0 = ()
+    fn0 = function %foo()
 
     ss0 = incoming_arg 8, offset 0
     ss1 = incoming_arg 1024, offset -1024

cranelift/filetests/isa/intel/legalize-memory.cton

@@ -76,9 +76,9 @@ ebb0(v0: i32, v999: i64):
     ; check: $ebb0(
     ; nextln:     trap heap_oob
     ; check: ebb1:
-    ; nextln:     v2 = iconst.i64 0
-    ; nextln:     v3 = load.f32 v2+16
-    ; nextln:     return v3
+    ; nextln:     v1 = iconst.i64 0
+    ; nextln:     v2 = load.f32 v1+16
+    ; nextln:     return v2
     ; nextln: }
     v1 = heap_addr.i64 heap0, v0, 0x1000_0001
     v2 = load.f32 v1+16