compiler: emit non-PIE executables

This fixes a problem on baremetal targets, where PIE doesn't make any
sense. Specifically, on ARM, the compiler sometimes inserted GOT
pointers for linker-defined globals.

compiler.go

@@ -93,7 +93,7 @@ func NewCompiler(pkgName, triple string, dumpSSA bool) (*Compiler, error) {
 	if err != nil {
 		return nil, err
 	}
-	c.machine = target.CreateTargetMachine(triple, "", "", llvm.CodeGenLevelDefault, llvm.RelocPIC, llvm.CodeModelDefault)
+	c.machine = target.CreateTargetMachine(triple, "", "", llvm.CodeGenLevelDefault, llvm.RelocStatic, llvm.CodeModelDefault)
 	c.targetData = c.machine.CreateTargetData()
 
 	c.mod = llvm.NewModule(pkgName)

target.go

@@ -28,6 +28,7 @@ func LoadTarget(target string) (*TargetSpec, error) {
 		Triple:      target,
 		BuildTags:   []string{runtime.GOOS, runtime.GOARCH},
 		Linker:      "cc",
+		PreLinkArgs: []string{"-no-pie"}, // WARNING: clang < 5.0 requires -nopie
 		Objcopy:     "objcopy",
 	}