Fix redefinition of CONF_ARCH_STRING for ARM architectures

The macro `__ARM_ARCH` is defined both for 32-bit and 64-bit ARM so it cannot be used to identify ARM64. Now `__ARM_ARCH_ISA_A64` is used instead, which should only be defined for ARM64. This caused a warning due to the macro `CONF_ARCH_STRING` being redefined when compiling for Android. Furthermore, support for detecting big-endian ARM64 with the `__ARM_BIG_ENDIAN` macro is added.

See https://developer.arm.com/documentation/dui0774/g/chr1383660321827

src/base/detect.h

@@ -163,19 +163,19 @@
 #define CONF_ARCH_ARM 1
 #define CONF_ARCH_STRING "arm"
 #define CONF_ARCH_ENDIAN_BIG 1
-#endif
-
-#if defined(__ARMEL__)
+#elif defined(__ARMEL__)
 #define CONF_ARCH_ARM 1
 #define CONF_ARCH_STRING "arm"
 #define CONF_ARCH_ENDIAN_LITTLE 1
-#endif
-
-#if defined(__aarch64__) || defined(__arm64__) || defined(__ARM_ARCH)
+#elif defined(__aarch64__) || defined(__arm64__) || defined(__ARM_ARCH_ISA_A64)
 #define CONF_ARCH_ARM64 1
 #define CONF_ARCH_STRING "arm64"
+#if defined(__ARM_BIG_ENDIAN)
+#define CONF_ARCH_ENDIAN_BIG 1
+#else
 #define CONF_ARCH_ENDIAN_LITTLE 1
 #endif
+#endif
 
 #ifndef CONF_FAMILY_STRING
 #define CONF_FAMILY_STRING "unknown"