Make lib64 clang include path check more robust.

On Fedora 33+, there is a buggy package that installs to
`/usr/lib64/clang/{version}/lib`, even on 32-bit systems. The original
code sees the `/usr/lib64/clang/{version}` directory, checks for an
`include` subdirectory, and then gives up because it doesn't exist.

To be more robust, check both `/usr/lib64/clang/{version}/include` and
`/usr/lib/clang/{version}/include`, and only allow versions that match
the LLVM major version used to build tinygo.

builder/env.go

@@ -6,6 +6,9 @@ import (
 	"os/exec"
 	"path/filepath"
 	"sort"
+	"strings"
+
+	"tinygo.org/x/go-llvm"
 )
 
 // getClangHeaderPath returns the path to the built-in Clang headers. It tries
@@ -26,6 +29,7 @@ func getClangHeaderPath(TINYGOROOT string) string {
 
 	// It looks like we are built with a system-installed LLVM. Do a last
 	// attempt: try to use Clang headers relative to the clang binary.
+	llvmMajor := strings.Split(llvm.Version, ".")[0]
 	for _, cmdName := range commands["clang"] {
 		binpath, err := exec.LookPath(cmdName)
 		if err == nil {
@@ -43,25 +47,35 @@ func getClangHeaderPath(TINYGOROOT string) string {
 			//     /usr/lib/llvm-9/lib64/clang/9.0.1/include/
 			llvmRoot := filepath.Dir(filepath.Dir(binpath))
 			clangVersionRoot := filepath.Join(llvmRoot, "lib64", "clang")
-			dirs, err := ioutil.ReadDir(clangVersionRoot)
-			if err != nil {
+			dirs64, err64 := ioutil.ReadDir(clangVersionRoot)
 			// Example include path:
 			//     /usr/lib/llvm-9/lib/clang/9.0.1/include/
 			clangVersionRoot = filepath.Join(llvmRoot, "lib", "clang")
-				dirs, err = ioutil.ReadDir(clangVersionRoot)
-				if err != nil {
+			dirs32, err32 := ioutil.ReadDir(clangVersionRoot)
+			if err64 != nil && err32 != nil {
 				// Unexpected.
 				continue
 			}
+			dirnames := make([]string, len(dirs64)+len(dirs32))
+			dirCount := 0
+			for _, d := range dirs32 {
+				name := d.Name()
+				if name == llvmMajor || strings.HasPrefix(name, llvmMajor+".") {
+					dirnames[dirCount] = filepath.Join(llvmRoot, "lib", "clang", name)
+					dirCount++
+				}
+			}
+			for _, d := range dirs64 {
+				name := d.Name()
+				if name == llvmMajor || strings.HasPrefix(name, llvmMajor+".") {
+					dirnames[dirCount] = filepath.Join(llvmRoot, "lib64", "clang", name)
+					dirCount++
 				}
-			dirnames := make([]string, len(dirs))
-			for i, d := range dirs {
-				dirnames[i] = d.Name()
 			}
 			sort.Strings(dirnames)
 			// Check for the highest version first.
-			for i := len(dirnames) - 1; i >= 0; i-- {
-				path := filepath.Join(clangVersionRoot, dirnames[i], "include")
+			for i := dirCount - 1; i >= 0; i-- {
+				path := filepath.Join(dirnames[i], "include")
 				_, err := os.Stat(filepath.Join(path, "stdint.h"))
 				if err == nil {
 					return path