util: detect LoongArch architecture

Only 64-bit is considered now because 32-bit LoongArch Linux support
doesn't exist in upstream yet.

Signed-off-by: Icenowy Zheng <uwu@icenowy.me>
Reviewed-by: Dave Airlie <airlied@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/30197>

src/util/detect_arch.h

@@ -112,6 +112,14 @@
 #endif
 #endif
 
+#if defined(__loongarch__)
+#ifdef __loongarch_lp64
+#define DETECT_ARCH_LOONGARCH64 1
+#else
+#error "detect_arch: unknown target loongarch base ABI type"
+#endif
+#endif
+
 #ifndef DETECT_ARCH_X86
 #define DETECT_ARCH_X86 0
 #endif
@@ -168,4 +176,8 @@
 #define DETECT_ARCH_RISCV64 0
 #endif
 
+#ifndef DETECT_ARCH_LOONGARCH64
+#define DETECT_ARCH_LOONGARCH64 0
+#endif
+
 #endif /* UTIL_DETECT_ARCH_H_ */