Fix macOS build with Xcode 15.4 and -arch arm64, see also 8a384af

Fixes rurban#284 by disabling PMP_Multilinear not only on aarch64, but also
on arm64. Those are the same things under different labels.

CMakeLists.txt

@@ -60,6 +60,13 @@ elseif ((CMAKE_SYSTEM_PROCESSOR STREQUAL "arm")
   add_definitions(-DHAVE_NEON)
 endif()
 
+if ((CMAKE_SYSTEM_PROCESSOR STREQUAL "aarch64")   # GNU and others
+    OR (CMAKE_SYSTEM_PROCESSOR STREQUAL "arm64")) # macOS
+  set(SYSTEM_PROCESSOR_IS_AARCH64 TRUE)
+else()
+  set(SYSTEM_PROCESSOR_IS_AARCH64 FALSE)
+endif()
+
 # TODO: rather parse `$CC -march=native -dM -E - <<< ''` [GH #10]
 if(NOT CMAKE_CROSSCOMPILING)
   if(CMAKE_SYSTEM_NAME MATCHES "Linux")
@@ -324,7 +331,7 @@ else(AVX512VL_TRUE)
 endif(AVX512VL_TRUE)
 
 if(CMAKE_CROSSCOMPILING)
-  if(CMAKE_SYSTEM_PROCESSOR STREQUAL "aarch64")
+  if(SYSTEM_PROCESSOR_IS_AARCH64)
     set(SSE2_FOUND true)
     set(SSE42_FOUND true)
   elseif(CMAKE_SYSTEM_PROCESSOR STREQUAL "x86_64")
@@ -470,13 +477,13 @@ if(SSE42_FOUND)
       list(APPEND X86_64ONLY_SRC metrohash/metrohash64crc.cpp
            metrohash/metrohash128crc.cpp)
     endif()
-    if(NOT (CMAKE_SYSTEM_PROCESSOR STREQUAL "aarch64") AND NOT MSVC)
+    if(NOT SYSTEM_PROCESSOR_IS_AARCH64 AND NOT MSVC)
       list(APPEND X86_64ONLY_SRC crc32_hw1.c)
     endif()
   else()
     message(STATUS "32bit only: CMAKE_SIZEOF_VOID_P=${CMAKE_SIZEOF_VOID_P}")
   endif()
-  if(CMAKE_SYSTEM_PROCESSOR STREQUAL "aarch64")
+  if(SYSTEM_PROCESSOR_IS_AARCH64)
     set(SIPHASH_SRC siphash.c)
   else()
     set(SIPHASH_SRC siphash_ssse3.c)
@@ -574,7 +581,7 @@ endif()
 set(BLAKE3_SRC blake3/blake3.c blake3/blake3_dispatch.c
                blake3/blake3_portable.c)
 if(SSE42_FOUND)
-  if(CMAKE_SYSTEM_PROCESSOR STREQUAL "aarch64")
+  if(SYSTEM_PROCESSOR_IS_AARCH64)
     set(BLAKE3_SRC ${BLAKE3_SRC} blake3/blake3_neon.c)
   else()
     set(BLAKE3_SRC ${BLAKE3_SRC} blake3/blake3_sse41.c)
@@ -618,7 +625,7 @@ if(CMAKE_CROSSCOMPILING)
   unset(PMPML_SRC)
   set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -DCROSSCOMPILING")
 endif()
-if(CMAKE_SYSTEM_PROCESSOR STREQUAL "aarch64")
+if(SYSTEM_PROCESSOR_IS_AARCH64)
   #HAVE_SSE42
   unset(PMPML_SRC)
 endif()