c_abi tests: allow passing standard target options

test/stage1/c_abi/build.zig

@@ -2,15 +2,18 @@ const Builder = @import("std").build.Builder;
 
 pub fn build(b: *Builder) void {
     const rel_opts = b.standardReleaseOptions();
+    const target = b.standardTargetOptions(.{});
 
     const c_obj = b.addObject("cfuncs", null);
     c_obj.addCSourceFile("cfuncs.c", &[_][]const u8{"-std=c99"});
     c_obj.setBuildMode(rel_opts);
     c_obj.linkSystemLibrary("c");
+    c_obj.target = target;
 
     const main = b.addTest("main.zig");
     main.setBuildMode(rel_opts);
     main.addObject(c_obj);
+    main.target = target;
 
     const test_step = b.step("test", "Test the program");
     test_step.dependOn(&main.step);