compiler: really define runtime.mem* as LLVM intrinsic wrappers

This makes it possible to //go:linkname them from other places, like in
the reflect package. And is in my opinion a much cleaner solution.

src/runtime/runtime.go

@@ -26,19 +26,19 @@ func GOROOT() string {
 }
 
 // Copy size bytes from src to dst. The memory areas must not overlap.
-// Calls to this function are converted to LLVM intrinsic calls such as
-// llvm.memcpy.p0i8.p0i8.i32(dst, src, size, false).
+// This function is implemented by the compiler as a call to a LLVM intrinsic
+// like llvm.memcpy.p0i8.p0i8.i32(dst, src, size, false).
 func memcpy(dst, src unsafe.Pointer, size uintptr)
 
 // Copy size bytes from src to dst. The memory areas may overlap and will do the
 // correct thing.
-// Calls to this function are converted to LLVM intrinsic calls such as
-// llvm.memmove.p0i8.p0i8.i32(dst, src, size, false).
+// This function is implemented by the compiler as a call to a LLVM intrinsic
+// like llvm.memmove.p0i8.p0i8.i32(dst, src, size, false).
 func memmove(dst, src unsafe.Pointer, size uintptr)
 
 // Set the given number of bytes to zero.
-// Calls to this function are converted to LLVM intrinsic calls such as
-// llvm.memset.p0i8.i32(ptr, 0, size, false).
+// This function is implemented by the compiler as a call to a LLVM intrinsic
+// like llvm.memset.p0i8.i32(ptr, 0, size, false).
 func memzero(ptr unsafe.Pointer, size uintptr)
 
 // This intrinsic returns the current stack pointer.