add CrossTarget.getObjectFormat

closes #4588

thanks Michaël Larouche for the suggested fix

Author: andrewrk

lib/std/target.zig

@@ -1014,18 +1014,22 @@ pub const Target = struct {
         return libPrefix_cpu_arch_abi(self.cpu.arch, self.abi);
     }
 
-    pub fn getObjectFormat(self: Target) ObjectFormat {
-        if (self.os.tag == .windows or self.os.tag == .uefi) {
+    pub fn getObjectFormatSimple(os_tag: Os.Tag, cpu_arch: Cpu.Arch) ObjectFormat {
+        if (os_tag == .windows or os_tag == .uefi) {
             return .coff;
-        } else if (self.isDarwin()) {
+        } else if (os_tag.isDarwin()) {
             return .macho;
         }
-        if (self.cpu.arch.isWasm()) {
+        if (cpu_arch.isWasm()) {
             return .wasm;
         }
         return .elf;
     }
 
+    pub fn getObjectFormat(self: Target) ObjectFormat {
+        return getObjectFormatSimple(self.os.tag, self.cpu.arch);
+    }
+
     pub fn isMinGW(self: Target) bool {
         return self.os.tag == .windows and self.isGnu();
     }

lib/std/zig/cross_target.zig

@@ -645,6 +645,10 @@ pub const CrossTarget = struct {
         self.glibc_version = SemVer{ .major = major, .minor = minor, .patch = patch };
     }
 
+    pub fn getObjectFormat(self: CrossTarget) ObjectFormat {
+        return Target.getObjectFormatSimple(self.getOsTag(), self.getCpuArch());
+    }
+
     fn updateCpuFeatures(self: CrossTarget, set: *Target.Cpu.Feature.Set) void {
         set.removeFeatureSet(self.cpu_features_sub);
         set.addFeatureSet(self.cpu_features_add);