add standalone tests for the new linker bug fixes

This is just a temp addition until I figure out how to tweak
the stage2 test harness to add the ability to test the linker too.

test/standalone.zig

@@ -34,6 +34,10 @@ pub fn addCases(cases: *tests.StandaloneContext) void {
     cases.addBuildFile("test/standalone/link_frameworks/build.zig", .{
         .requires_macos_sdk = true,
     });
+    cases.addBuildFile("test/standalone/link_common_symbols_alignment/build.zig", .{});
+    if (builtin.os.tag == .macos) {
+        cases.addBuildFile("test/standalone/link_import_tls_dylib/build.zig", .{});
+    }
     cases.addBuildFile("test/standalone/issue_339/build.zig", .{});
     cases.addBuildFile("test/standalone/issue_8550/build.zig", .{});
     cases.addBuildFile("test/standalone/issue_794/build.zig", .{});

test/standalone/link_common_symbols_alignment/a.c

@@ -0,0 +1,2 @@
+int foo;
+__attribute__((aligned(4096))) int bar;

test/standalone/link_common_symbols_alignment/build.zig

@@ -0,0 +1,16 @@
+const Builder = @import("std").build.Builder;
+
+pub fn build(b: *Builder) void {
+    const mode = b.standardReleaseOptions();
+
+    const lib_a = b.addStaticLibrary("a", null);
+    lib_a.addCSourceFiles(&.{"a.c"}, &.{"-fcommon"});
+    lib_a.setBuildMode(mode);
+
+    const test_exe = b.addTest("main.zig");
+    test_exe.setBuildMode(mode);
+    test_exe.linkLibrary(lib_a);
+
+    const test_step = b.step("test", "Test it");
+    test_step.dependOn(&test_exe.step);
+}

test/standalone/link_common_symbols_alignment/main.zig

@@ -0,0 +1,9 @@
+const std = @import("std");
+
+extern var foo: i32;
+extern var bar: i32;
+
+test {
+    try std.testing.expect(@ptrToInt(&foo) % 4 == 0);
+    try std.testing.expect(@ptrToInt(&bar) % 4096 == 0);
+}

test/standalone/link_import_tls_dylib/a.c

@@ -0,0 +1 @@
+_Thread_local int a;

test/standalone/link_import_tls_dylib/build.zig

@@ -0,0 +1,16 @@
+const Builder = @import("std").build.Builder;
+
+pub fn build(b: *Builder) void {
+    const mode = b.standardReleaseOptions();
+
+    const lib = b.addSharedLibrary("a", null, b.version(1, 0, 0));
+    lib.setBuildMode(mode);
+    lib.addCSourceFile("a.c", &.{});
+
+    const test_exe = b.addTest("main.zig");
+    test_exe.setBuildMode(mode);
+    test_exe.linkLibrary(lib);
+
+    const test_step = b.step("test", "Test it");
+    test_step.dependOn(&test_exe.step);
+}

test/standalone/link_import_tls_dylib/main.zig

@@ -0,0 +1,7 @@
+const std = @import("std");
+
+extern threadlocal var a: i32;
+
+test {
+    try std.testing.expect(a == 0);
+}