add test for spawning child process with empty environment

thanks to BenoitJGirard for pointing out the child process
implementation needs 3 extra null bytes in #2031

std/build.zig

@@ -1530,6 +1530,12 @@ pub const RunStep = struct {
         }
     }
 
+    pub fn clearEnvironment(self: *RunStep) void {
+        const new_env_map = self.builder.allocator.create(BufMap) catch unreachable;
+        new_env_map.* = BufMap.init(self.builder.allocator);
+        self.env_map = new_env_map;
+    }
+
     pub fn addPathDir(self: *RunStep, search_path: []const u8) void {
         const PATH = if (builtin.os == builtin.Os.windows) "Path" else "PATH";
         const env_map = self.getEnvMap();

test/build_examples.zig

@@ -19,6 +19,7 @@ pub fn addCases(cases: *tests.BuildExamplesContext) void {
     cases.addBuildFile("test/standalone/pkg_import/build.zig");
     cases.addBuildFile("test/standalone/use_alias/build.zig");
     cases.addBuildFile("test/standalone/brace_expansion/build.zig");
+    cases.addBuildFile("test/standalone/empty_env/build.zig");
     if (false) {
         // TODO this test is disabled because it is failing on the CI server's linux. when this is fixed
         // enable it for at least linux

test/standalone/empty_env/build.zig

@@ -0,0 +1,12 @@
+const Builder = @import("std").build.Builder;
+
+pub fn build(b: *Builder) void {
+    const main = b.addExecutable("main", "main.zig");
+    main.setBuildMode(b.standardReleaseOptions());
+
+    const run = main.run();
+    run.clearEnvironment();
+
+    const test_step = b.step("test", "Test it");
+    test_step.dependOn(&run.step);
+}

test/standalone/empty_env/main.zig

@@ -0,0 +1,6 @@
+const std = @import("std");
+
+pub fn main() void {
+    const env_map = std.os.getEnvMap(std.debug.global_allocator) catch @panic("unable to get env map");
+    std.testing.expect(env_map.count() == 0);
+}