--target: windows, linux, arm64, macos or a triple, in the compiler written in Finch

Targets, the target's C compiler (FINCH_CC) for linking, C import for the target (--target to libclang, its
headers), the AAPCS64 and Microsoft x64 ways of passing structs by value (and the System V one),
dllexport for libraries on Windows, .exe names, and running the program through wine or qemu-aarch64.
std/ gets time_windows.fch and proc_windows.fch: a module has a version per system (name_windows.fch,
name_macos.fch, name_linux.fch) that wins over name.fch. stdin, stdout and stderr work where C makes them macros.

Run for real: all 27 programs under tests/run and tests/new pass on ARM64 Linux under qemu and on Windows
under Wine (MinGW), structs by value and callbacks included. macOS is only checked as far as clang accepts the
IR; there is no emulator for it here.

std/finch_win.h

@@ -0,0 +1,6 @@
+/* The Windows functions std/time_windows.fch needs. Declared here, not by including <windows.h>:
+   libclang can't parse that header with MinGW's intrinsics. Both are in kernel32. */
+unsigned long long GetTickCount64(void);
+void Sleep(unsigned long milliseconds);
+int QueryPerformanceCounter(long long *count);
+int QueryPerformanceFrequency(long long *frequency);

std/proc_windows.fch

@@ -0,0 +1,45 @@
+// Programs, for Windows. The same functions as proc.fch (that file is for Linux and macOS).
+import "stdlib.h"
+import "process.h"
+import "direct.h"
+import "time.h"
+
+fn run(str command) -> int {
+    return shell(command)
+}
+
+fn output(str command) -> str! {
+    tmp := proc_env("TEMP", ".") + "\\finch_out_" + str(getpid()) + "_" + str(int(time(null)))
+    code := shell(command + " > \"" + tmp + "\" 2>&1")
+    text := read_file(tmp) or ""
+    delete_file(tmp)
+    if code != 0 {
+        return error("'" + command + "' exited with code " + str(code) + ": " + text.trim())
+    }
+    return text
+}
+
+fn proc_env(str name, str fallback) -> str {
+    v := getenv(name)
+    if v.len == 0 {
+        return fallback
+    }
+    return v
+}
+
+fn env(str name, str fallback) -> str {
+    return proc_env(name, fallback)
+}
+
+fn pid() -> int {
+    return int(getpid())
+}
+
+fn cwd() -> str {
+    []char buf
+    for i in 0..4096 {
+        buf.push(char(0))
+    }
+    getcwd(buf.ptr, 4096)
+    return str(buf.ptr)
+}

std/time_windows.fch

@@ -0,0 +1,75 @@
+// Time, for Windows. The same functions as time.fch (that file is for Linux and macOS).
+import "time.h"
+import "finch_win.h"
+
+struct Date {
+    int year
+    int month       // 1 to 12
+    int day         // 1 to 31
+    int hour
+    int minute
+    int second
+    int weekday     // 0 is Sunday
+    int yearday     // 1 to 366
+}
+
+fn now() -> int {
+    return int(time(null))
+}
+
+// milliseconds on a clock that only goes forward (the performance counter: GetTickCount64 ticks every 15 ms)
+fn millis() -> int {
+    i64 count = 0
+    i64 freq = 1
+    QueryPerformanceFrequency(addr(freq))
+    QueryPerformanceCounter(addr(count))
+    return int(count / freq) * 1000 + int(count % freq) * 1000 / int(freq)
+}
+
+fn sleep(int ms) {
+    Sleep(u32(ms))
+}
+
+fn parts(tm t) -> Date {
+    return Date(year: int(t.tm_year) + 1900, month: int(t.tm_mon) + 1, day: int(t.tm_mday), hour: int(t.tm_hour),
+                minute: int(t.tm_min), second: int(t.tm_sec), weekday: int(t.tm_wday), yearday: int(t.tm_yday) + 1)
+}
+
+fn date(int unix) -> Date {
+    tm t
+    i64 stamp = unix
+    _gmtime64_s(addr(t), addr(stamp))
+    return parts(t)
+}
+
+fn local(int unix) -> Date {
+    tm t
+    i64 stamp = unix
+    _localtime64_s(addr(t), addr(stamp))
+    return parts(t)
+}
+
+fn format(int unix, str pattern) -> str {
+    tm t
+    i64 stamp = unix
+    _localtime64_s(addr(t), addr(stamp))
+    []char buf
+    for i in 0..256 {
+        buf.push(char(0))
+    }
+    strftime(buf.ptr, 256, pattern, addr(t))
+    return str(buf.ptr)
+}
+
+fn days_in_month(int year, int month) -> int {
+    if month == 2 {
+        if year % 4 == 0 && (year % 100 != 0 || year % 400 == 0) {
+            return 29
+        }
+        return 28
+    }
+    if month == 4 || month == 6 || month == 9 || month == 11 {
+        return 30
+    }
+    return 31
+}