[svrplus] svrplus.c: Register for arm64 and arm64ec on Win11 build 21…

…262 or later; for earlier versions, only arm64.

ARM64EC was added at the same time as general amd64 emulation in
Windows 11 build 21277 (actually 21262, a leaked build).

On Windows 10, don't register for either amd64 or arm64ec.

See #398: Installing on ARM64 shows an error that the AMD64 version
of the DLL couldn't be registered
Reported by @kristibektashi.

NEWS.md

@@ -127,8 +127,10 @@
   * Windows: The "xattr" tab now respects the LC_ALL and/or LC_MESSAGES
     environment variable to allow for easier multi-language testing.
   * Windows: On ARM64 Windows 11, register for i386, arm64, and arm64ec.
-    * On ARM64 Windows 10, only register amd64 if using build 21277 or later.
-    * Fixes Fixes #398: Installing on ARM64 shows an error that the AMD64 version of the DLL couldn't be registered
+    * Only if using build 21262 or later. (RTM is 22000)
+    * On earlier versions, only arm64 will be registered, since ARM64EC
+      was added at the same time as amd64 emulation.
+    * Fixes #398: Installing on ARM64 shows an error that the AMD64 version of the DLL couldn't be registered
       * Reported by @kristibektashi.
 
 ## v2.2.1 (released 2023/07/30)

src/libwin32common/rp_versionhelpers.h

@@ -102,10 +102,11 @@ VERSIONHELPERAPI IsWindowsVersionOrGreater_BuildNumberCheck(WORD major, WORD min
             VER_BUILDNUMBER, VER_GREATER_EQUAL));
 }
 
-VERSIONHELPERAPI IsWindows10Build21277OrGreater(void) {
-    // Windows 10 Build 21277 on ARM added amd64 emulation.
+VERSIONHELPERAPI IsWindows11Build21262OrGreater(void) {
+    // Windows 11 pre-release Build 21262 on ARM added amd64 emulation.
+    // NOTE: Officially it was 21277, but 21262 was leaked and supports it too.
     // https://blogs.windows.com/windows-insider/2020/12/10/introducing-x64-emulation-in-preview-for-windows-10-on-arm-pcs-to-the-windows-insider-program/
-    IsWindowsVersionOrGreater_BuildNumberCheck(HIBYTE(0x0A00), LOBYTE(0x0A00), 21277);
+    IsWindowsVersionOrGreater_BuildNumberCheck(HIBYTE(0x0A00), LOBYTE(0x0A00), 21262);
 }
 
 VERSIONHELPERAPI IsWindows11OrGreater(void) {

src/svrplus/svrplus.c

@@ -1141,20 +1141,15 @@ static int check_system_architectures(void)
 				g_archs[g_arch_count++] = CPU_arm;
 				break;
 			case CPU_arm64:
-				// Windows 10 on ARM RTM only supports i386 emulation.
-				// - Build 21277: Added amd64 emulation.
-				// - Build 22000 (Win11): Added arm64ec.
+				// Windows 10 on ARM only supports i386 emulation.
+				// Windows 11 added amd64 emulation and arm64ec.
 				// https://blogs.windows.com/windows-insider/2020/12/10/introducing-x64-emulation-in-preview-for-windows-10-on-arm-pcs-to-the-windows-insider-program/
-				if (IsWindows11OrGreater()) {
-					// Add arm64 and arm64ec.
+				if (IsWindows11Build21262OrGreater()) {
+					// Windows 11 with amd64 emulation: Add arm64 and arm64ec.
 					g_archs[g_arch_count++] = CPU_arm64;
 					g_archs[g_arch_count++] = CPU_arm64ec;
-				} else if (IsWindows10Build21277OrGreater()) {
-					// Add amd64 and arm64.
-					g_archs[g_arch_count++] = CPU_amd64;
-					g_archs[g_arch_count++] = CPU_arm64;
 				} else {
-					// Just add arm64.
+					// Windows 10 with i386 emulation only: Just add arm64.
 					g_archs[g_arch_count++] = CPU_arm64;
 				}
 				break;