fix: match diagnostics by format instead of OS

[Left-Hand]

Problem

ProblemList.diagnose() picks which regex to use based on the OS:

const isWin = os.platform() == "win32";
let matches = isWin ? rOutputMsvc.exec(textLine) : rOutputGcc.exec(textLine);

This assumes Windows ⇒ MSVC and non-Windows ⇒ GCC/Clang. But on Windows it is common to use a GCC or Clang toolchain (e.g. cross-compilers like riscv32-wch-elf-gcc, arm-none-eabi-gcc, or plain MinGW/Clang). In that case every GCC/Clang diagnostic line is pushed through the MSVC regex, which cannot match file:line:col: error: message, so all errors/warnings are silently dropped from the Problems panel.

Fix

Match by format instead of by OS: try the GCC/Clang regex first, then fall back to the MSVC regex.

let matches = rOutputGcc.exec(textLine);
let isGcc = true;
if (!matches) {
    matches = rOutputMsvc.exec(textLine);
    isGcc = false;
}

Why this is safe for MSVC users

The two regexes are mutually exclusive in practice:

• The GCC regex requires a :line:col: sequence followed by error|warning, e.g. file.cpp:12:5: error: ....
• The MSVC regex requires (line): error C1234: ... / warning C1234: ....

MSVC's file(line): error C1234: msg shape has no :line:col: sequence, so the GCC regex never matches it and it still falls through to the MSVC regex — behavior for MSVC users is unchanged. The only behavioral change is that GCC/Clang diagnostics now work on Windows.

Validation

• npm run compile passes cleanly.
• Manually verified the dispatch against representative GCC, Clang, and MSVC lines (GCC/Clang → GCC regex; MSVC → MSVC regex; no cross-match).

This is the companion fix to the logfile CRLF / control-char fixes already submitted to xmake-io/xmake (#7711, #7712), which make the XMAKE_LOGFILE content parseable. This PR fixes the other half of the pipeline — the regex that consumes it.