Run test262 tests in CI

Run test262 tests for Linux, macOS and Cosmopolitan

Add a Makefile `test2-bootstrap` helper to clone and patch test262 tests at
a particular commit. Running with the latest commit noticed a few tests were
failing and added them to the errors list.

The CI environment, especially for macOS, was a bit more unpredictable and was
failing in atomics tests due to lower timeouts in the `atomicsHelper` so double
the timeouts. The time didn't worsen too much. It still takes about 2-3 min.

Makefile

@@ -54,6 +54,10 @@ PREFIX?=/usr/local
 # use UB sanitizer
 #CONFIG_UBSAN=y
 
+# TEST262 bootstrap config: commit id and shallow "since" parameter
+TEST262_COMMIT?=a5e69a1534de88d1eb29b76657d84c8541b72df7
+TEST262_SINCE?=2025-09-01
+
 OBJDIR=.obj
 
 ifdef CONFIG_ASAN
@@ -464,6 +468,15 @@ stats: qjs$(EXE)
 microbench: qjs$(EXE)
 	$(WINE) ./qjs$(EXE) --std tests/microbench.js
 
+ifeq ($(wildcard test262/features.txt),)
+test2-bootstrap:
+	git clone --single-branch --shallow-since=$(TEST262_SINCE) https://github.com/tc39/test262.git
+	(cd test262 && git checkout -q $(TEST262_COMMIT) && patch -p1 < ../tests/test262.patch && cd ..)
+else
+test2-bootstrap:
+	(cd test262 && git fetch && git reset --hard $(TEST262_COMMIT) && patch -p1 < ../tests/test262.patch && cd ..)
+endif
+
 ifeq ($(wildcard test262o/tests.txt),)
 test2o test2o-update:
 	@echo test262o tests not installed