fix(goobj): make R_DWTXTADDR_U4 relocation type Go-version-aware

The relocation type number shifted between Go 1.26 (103) and Go 1.27
(106)
because new LoongArch relocations were inserted. Detect the Go version
at
runtime and use the correct value.

asm/goobj.go

@@ -10,6 +10,7 @@ import (
 	"os"
 	"os/exec"
 	"path/filepath"
+	"strings"
 	"sync"
 )
 
@@ -90,12 +91,50 @@ const (
 )
 
 // Relocation types (cmd/internal/objabi).
+// R_PCREL and R_ADDR are stable across Go versions.
 const (
-	relocPCRel       = 14  // R_PCREL
-	relocAddr        = 1   // R_ADDR
-	relocDWTXTADDRU4 = 106 // R_DWTXTADDR_U4
+	relocPCRel = 14 // R_PCREL
+	relocAddr  = 1  // R_ADDR
 )
 
+// relocDWTXTADDRU4 returns the R_DWTXTADDR_U4 relocation type for the
+// installed Go toolchain.  The value shifted between Go 1.26 (103) and
+// Go 1.27 (106) because new LoongArch relocations were inserted before it.
+func relocDWTXTADDRU4() uint16 {
+	if isGo127OrLater() {
+		return 106
+	}
+	return 103
+}
+
+var (
+	goVersionOnce sync.Once
+	goVersionGT26 bool
+)
+
+// isGo127OrLater reports whether the installed Go toolchain is 1.27 or later.
+func isGo127OrLater() bool {
+	goVersionOnce.Do(func() {
+		goBin, err := exec.LookPath("go")
+		if err != nil {
+			return
+		}
+		out, err := exec.Command(goBin, "version").Output()
+		if err != nil {
+			return
+		}
+		// "go version go1.27rc1 linux/amd64"
+		s := string(out)
+		for _, prefix := range []string{"go version go1.27", "go version go1.28", "go version go1.29", "go version go2."} {
+			if strings.Contains(s, prefix) {
+				goVersionGT26 = true
+				return
+			}
+		}
+	})
+	return goVersionGT26
+}
+
 // Special package indices for symbol references.
 const (
 	pkgIdxNone = 0x7fffffff