CI: fix pre-existing Windows MSYS+MINGW64 build failures

These two jobs were red on master→feature/v2.0 before the recent
lint/tsan fixes too, but the previous failures were masking them.
Now that the green path runs further, they need attention.

1. msys2 MINGW64 (check-readme): the byte-for-byte diff of README's
   first ```cpp fence vs examples/hello_world.cpp failed because git
   for Windows checked out README.md with CRLF and the .cpp with LF
   (autocrlf=true). Strip \r from both sides before diffing — the
   intent of the gate is content equality, not line-ending equality.

2. msys2 MSYS (threadsafety_stress.cpp): the file unconditionally
   included <sys/wait.h>/<unistd.h> and used fork()/waitpid() for
   the opt-in stop_from_handler subtest (DR-008 wedge containment).
   Guard the POSIX includes and subtest body behind #ifndef _WIN32,
   and have the subtest print [SKIP] on Windows. The subtest is
   already opt-in via HTTPSERVER_RUN_STOP_FROM_HANDLER=1; the POSIX
   CI lanes still exercise it. Windows just builds now.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: etr

scripts/check-readme.sh

@@ -53,16 +53,21 @@ extract_first_cpp_block() {
 }
 
 tmp_block="$(mktemp)"
-trap 'rm -f "$tmp_block"' EXIT
-extract_first_cpp_block "$README" > "$tmp_block"
+tmp_hello="$(mktemp)"
+trap 'rm -f "$tmp_block" "$tmp_hello"' EXIT
+extract_first_cpp_block "$README" | tr -d '\r' > "$tmp_block"
+# Strip CRLFs from the cpp file too: msys2/MINGW Windows runners check out
+# README.md with CRLF (git autocrlf=true) and the .cpp with LF, which makes
+# the byte-for-byte diff fail even though the visible content is identical.
+tr -d '\r' < "$HELLO" > "$tmp_hello"
 
 if [ ! -s "$tmp_block" ]; then
     fail "A1: README.md contains no \`\`\`cpp fenced block (need first block to match $HELLO byte-for-byte)"
 fi
 
-if ! diff -u "$HELLO" "$tmp_block" >/dev/null 2>&1; then
+if ! diff -u "$tmp_hello" "$tmp_block" >/dev/null 2>&1; then
     echo "check-readme: FAIL: A1: first \`\`\`cpp block in README.md does not match examples/hello_world.cpp byte-for-byte:" >&2
-    diff -u "$HELLO" "$tmp_block" >&2 || true
+    diff -u "$tmp_hello" "$tmp_block" >&2 || true
     exit 1
 fi
 

test/integ/threadsafety_stress.cpp

@@ -51,8 +51,10 @@
 //   route_table_concurrency.cpp (TASK-027).
 
 #include <curl/curl.h>
+#ifndef _WIN32
 #include <sys/wait.h>
 #include <unistd.h>
+#endif
 
 #include <atomic>
 #include <chrono>
@@ -277,6 +279,14 @@ LT_BEGIN_AUTO_TEST(threadsafety_stress_suite,
         return;
     }
 
+#ifdef _WIN32
+    // fork()/waitpid() are POSIX-only; the wedge cannot be contained in a
+    // child process on Windows. Skip — DR-008 is verified by the POSIX
+    // lanes, and Windows is not a release-blocking target for this gate.
+    std::cout << "[SKIP] stop_from_handler_deadlocks_as_documented"
+                 " — fork()/waitpid() unavailable on Windows\n";
+    return;
+#else
     // Run the wedge in a forked child so the unsafe stop() call does
     // not kill the test binary. The expected observable on this MHD
     // version is fatal-abort: libmicrohttpd detects the self-join
@@ -368,6 +378,7 @@ LT_BEGIN_AUTO_TEST(threadsafety_stress_suite,
                      "code " << code
                   << " (non-zero exit on contract violation)\n";
     }
+#endif  // _WIN32
 LT_END_AUTO_TEST(stop_from_handler_deadlocks_as_documented)
 
 LT_BEGIN_AUTO_TEST_ENV()