all: remove remaining +build lines

builder/cc1as.cpp

@@ -1,4 +1,4 @@
-// +build byollvm
+//go:build byollvm
 
 //===-- cc1as.cpp - Clang Assembler  --------------------------------------===//
 //

builder/clang.cpp

@@ -1,4 +1,4 @@
-// +build byollvm
+//go:build byollvm
 
 #include <clang/Basic/DiagnosticOptions.h>
 #include <clang/CodeGen/CodeGenAction.h>

builder/lld.cpp

@@ -1,4 +1,4 @@
-// +build byollvm
+//go:build byollvm
 
 // This file provides C wrappers for liblld.
 

src/machine/machine_esp32c3_spi.go

@@ -1,5 +1,4 @@
 //go:build esp32c3
-// +build esp32c3
 
 package machine