util: Add DETECT_ARCH_ARM64EC for defined(_M_ARM64EC) equivalent

Signed-off-by: Yonggang Luo <luoyonggang@gmail.com>
Reviewed-by: Jesse Natalie <jenatali@microsoft.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/36744>

src/util/detect_arch.h

@@ -91,6 +91,10 @@
 #define DETECT_ARCH_AARCH64 1
 #endif
 
+#if defined(_M_ARM64EC)
+#define DETECT_ARCH_ARM64EC 1
+#endif
+
 #if defined(__mips64) && defined(__LP64__)
 #define DETECT_ARCH_MIPS64 1
 #endif
@@ -154,6 +158,10 @@
 #define DETECT_ARCH_AARCH64 0
 #endif
 
+#ifndef DETECT_ARCH_ARM64EC
+#define DETECT_ARCH_ARM64EC 0
+#endif
+
 #ifndef DETECT_ARCH_MIPS64
 #define DETECT_ARCH_MIPS64 0
 #endif