cmd/compile: more compact representation of DW_AT_high_pc
cmd/compile: more compact representation of DW_AT_high_pc

DWARF version 4 allows DW_AT_high_pc to be represented as a constant
offset from DW_AT_low_pc, this can help save up to 7 bytes per
function/lexical scope.

Change-Id: I93638d83638ecad4d0d1bfe27348eae6139820c9
Reviewed-on: https://go-review.googlesource.com/60530
Run-TryBot: Heschi Kreinick <e89ab2b172855aa0ad01c40c4d8a3535a61ac68a@google.com>
Reviewed-by: Heschi Kreinick <e89ab2b172855aa0ad01c40c4d8a3535a61ac68a@google.com>

nawawi/go,josharian/go,golang/go,polyverse-security/go,josharian/go,CAFxX/go,CAFxX/go,codestation/go,golang/go,cloudflare/go,codestation/go,Cofyc/go,golang/go,codestation/go,codestation/go,golang/go,CAFxX/go,codestation/go,cloudflare/go,golang/go,cloudflare/go,CAFxX/go,golang/go,golang/go,codestation/go,polyverse-security/go,cloudflare/go,cloudflare/go,CAFxX/go,nawawi/go,CAFxX/go,polyverse-security/go,josharian/go,Cofyc/go,akutz/go,polyverse-security/go,nawawi/go,nawawi/go,CAFxX/go,cloudflare/go,Cofyc/go,nawawi/go,akutz/go,codestation/go,nawawi/go,akutz/go,polyverse-security/go,Cofyc/go,polyverse-security/go,josharian/go,Cofyc/go,cloudflare/go,polyverse-security/go,Cofyc/go,codestation/go,akutz/go,polyverse-security/go,akutz/go,josharian/go,josharian/go,akutz/go,nawawi/go,josharian/go,akutz/go,cloudflare/go,CAFxX/go,golang/go,Cofyc/go,Cofyc/go,josharian/go,nawawi/go,akutz/go,christopher-henderson/Go