PXB-3210: PXB fails to build on macOS since 8.0.33-28 due to FIND_PRO…

…CPS()

https://jira.percona.com/browse/PXB-3210

The problem is FIND_PROCPS() will always fail on systems that don't use procps.
Now we verify that system is not macOS before running FIND_PROCPS().

storage/innobase/xtrabackup/src/CMakeLists.txt

@@ -21,7 +21,10 @@ OPTION(WITH_VERSION_CHECK "Build with version check" ON)
 INCLUDE(${MYSQL_CMAKE_SCRIPT_DIR}/compile_flags.cmake)
 
 FIND_GCRYPT()
-FIND_PROCPS()
+
+IF(NOT APPLE)
+  FIND_PROCPS()
+ENDIF()
 
 CHECK_TYPE_SIZE("unsigned long" SIZEOF_UNSIGNED_LONG)