main: switch to LLVM 10

This commit also adds a bit of version independence, in particular for
external commands. It also adds the LLVM version to the `tinygo version`
command, which might help while debugging.

builder/cc1as.h

@@ -11,8 +11,6 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "llvm/ADT/ArrayRef.h"
-
 /// Helper class for representing a single invocation of the assembler.
 struct AssemblerInvocation {
   /// @name Target Options
@@ -82,6 +80,7 @@ struct AssemblerInvocation {
   unsigned RelaxAll : 1;
   unsigned NoExecStack : 1;
   unsigned FatalWarnings : 1;
+  unsigned NoWarn : 1;
   unsigned IncrementalLinkerCompatible : 1;
   unsigned EmbedBitcode : 1;
 
@@ -107,6 +106,7 @@ public:
     RelaxAll = 0;
     NoExecStack = 0;
     FatalWarnings = 0;
+    NoWarn = 0;
     IncrementalLinkerCompatible = 0;
     DwarfVersion = 0;
     EmbedBitcode = 0;