[TD-3148] <feature>: make build system detect host arch. add other variables.

cmake/platform.inc

@@ -92,6 +92,14 @@ IF ("${CPUTYPE}" STREQUAL "")
   ELSEIF (CMAKE_SYSTEM_PROCESSOR MATCHES "armv7l")
     MESSAGE(STATUS "Set CPUTYPE to aarch32")
     SET(CPUTYPE "aarch32")
+    SET(TD_LINUX TRUE)
+    SET(TD_LINUX_32 FALSE)
+    SET(TD_ARM_32 TRUE)
+  ELSEIF (CMAKE_SYSTEM_PROCESSOR MATCHES "arm64")
+    SET(CPUTYPE "aarch64")
+    SET(TD_LINUX TRUE)
+    SET(TD_LINUX_64 FALSE)
+    SET(TD_ARM_64 TRUE)
   ENDIF ()
 
 ELSE ()