hash/crc32: add noescape tags to assembly functions

CRC-32 computation is stateless and the p slice does not get stored
anywhere. Thus, we mark the assembly functions as noescape so that
it doesn't believe that p leaks in:
	func Update(crc uint32, tab *Table, p []byte) uint32

Before:
	./crc32.go:153: leaking param: p

After:
	./crc32.go:153: Update p does not escape

Change-Id: I52ba35b6cc544fff724327140e0c27898431d1dc
Reviewed-on: https://go-review.googlesource.com/17069Reviewed-by: Russ Cox <rsc@golang.org>

src/hash/crc32/crc32_amd64.go

@@ -15,10 +15,12 @@ func haveCLMUL() bool
 
 // castagnoliSSE42 is defined in crc_amd64.s and uses the SSE4.2 CRC32
 // instruction.
+//go:noescape
 func castagnoliSSE42(crc uint32, p []byte) uint32
 
 // ieeeCLMUL is defined in crc_amd64.s and uses the PCLMULQDQ
 // instruction as well as SSE 4.1.
+//go:noescape
 func ieeeCLMUL(crc uint32, p []byte) uint32
 
 var sse42 = haveSSE42()

src/hash/crc32/crc32_amd64p32.go

@@ -13,6 +13,7 @@ func haveSSE42() bool
 
 // castagnoliSSE42 is defined in crc_amd64.s and uses the SSE4.2 CRC32
 // instruction.
+//go:noescape
 func castagnoliSSE42(crc uint32, p []byte) uint32
 
 var sse42 = haveSSE42()