Fix ABSL_RANDOM_RANDEN_COPTS setting on FreeBSD (#664)

* Fix build on FreeBSD

On FreeBSD amd64, both uname -p and uname -m returns amd64 (lowercase).
It seems Windows returns AMD64 (uppercase).

Reference:
[1] https://cmake.org/cmake/help/latest/variable/CMAKE_SYSTEM_PROCESSOR.html
[2] https://cmake.org/cmake/help/latest/variable/CMAKE_HOST_SYSTEM_PROCESSOR.html

* Use MATCHES for multiple values

absl/copts/AbseilConfigureCopts.cmake

@@ -12,7 +12,7 @@ else()
   set(ABSL_BUILD_DLL FALSE)
 endif()
 
-if("${CMAKE_SYSTEM_PROCESSOR}" STREQUAL "x86_64" OR "${CMAKE_SYSTEM_PROCESSOR}" STREQUAL "AMD64")
+if("${CMAKE_SYSTEM_PROCESSOR}" MATCHES "x86_64|amd64|AMD64")
   if (MSVC)
     set(ABSL_RANDOM_RANDEN_COPTS "${ABSL_RANDOM_HWAES_MSVC_X64_FLAGS}")
   else()