In pkg/runtime/funcdata.h, we currently have:

#define PCDATA_ArgSize 0 /* argument size at CALL instruction */
#define PCDATA_StackMapIndex 1

#define FUNCDATA_ArgsPointerMaps 2 /* garbage collector blocks */
#define FUNCDATA_LocalsPointerMaps 3
#define FUNCDATA_DeadValueMaps 4

However, PCDATA and FUNCDATA values live in logically distinct spaces, so there appears
to be no reason to not number the FUNCDATA values 0,1,2 instead of 2,3,4.  Further,
because the FUNCDATA values are used to index into a flat vector, not using the 0 and 1
entries means we leave holes in each function's pclntab entry.

On linux/amd64, changing the FUNCDATA values to 0,1,2 reduces the text segment size (as
reported by the binutils "size" utility) for "go" by ~104kB, for
"gofmt" by ~45kB, and for "camlistored" by ~208kB:

Before:
$ size go gofmt camlistored 
   text    data     bss     dec     hex filename
6506842  136996  105784 6749622  66fdb6 go
2376046   85232   90984 2552262  26f1c6 gofmt
17051050     190256  130320 17371626    10911ea camlistored

After:
$ size go gofmt camlistored 
   text    data     bss     dec     hex filename
6403034  136996  105784 6645814  656836 go
2331118   85232   90984 2507334  264246 gofmt
16842586     190256  130320 17163162    105e39a camlistored