build: bump minimum required mingw-w64 to v3.0 (from v1.0)

mingw-w64 3.0 was released on 2013-09-20. Offered by Debian jessie.

1.0 and 2.0 were released in 2011. It seems unlikely that many people
use them. The oldest downloadable toolchain (that I know of) comes with
3.0. Due to this, older versions weren't CI tested, and probably seldom
tested elsewhere. The last bugfix update for both 1.0 and 2.0 was
released in 2015.

curl can now assume availability of these 3.0 features/fixes:
- 64-bit file offsets.
- `ADDRESS_FAMILY` type.
- `__MINGW_PRINTF_FORMAT` macro. (in public curl headers)

Public curl headers keep supporting older mingw-w64 versions.

Fixes #17984
Closes #18010

lib/curl_setup.h

@@ -75,6 +75,11 @@
 #endif
 #endif
 
+#if defined(__MINGW32__) && \
+  (!defined(__MINGW64_VERSION_MAJOR) || (__MINGW64_VERSION_MAJOR < 3))
+#error "Building curl requires mingw-w64 3.0 or later"
+#endif
+
 /* Visual Studio 2008 is the minimum Visual Studio version we support.
    Workarounds for older versions of Visual Studio have been removed. */
 #if defined(_MSC_VER) && (_MSC_VER < 1500)

lib/easy_lock.h

@@ -30,12 +30,6 @@
 
 #if defined(_WIN32_WINNT) && _WIN32_WINNT >= 0x600
 
-#ifdef __MINGW32__
-#ifndef SRWLOCK_INIT
-#define SRWLOCK_INIT NULL
-#endif
-#endif /* __MINGW32__ */
-
 #define curl_simple_lock SRWLOCK
 #define CURL_SIMPLE_LOCK_INIT SRWLOCK_INIT