[BOLT][CMAKE] Check build target architecture for runtime libs

Account for cross-compilation build scenarios (X86 to ARM, Linux
to Windows, etc).

Reviewed By: rafauler

Differential Revision: https://reviews.llvm.org/D124712

Author: aaupov

bolt/CMakeLists.txt

@@ -5,7 +5,7 @@ set(BOLT_BINARY_DIR ${CMAKE_CURRENT_BINARY_DIR})
 set(CMAKE_CXX_STANDARD 14)
 
 set(BOLT_ENABLE_RUNTIME OFF)
-if (CMAKE_HOST_SYSTEM_PROCESSOR MATCHES "x86_64")
+if (CMAKE_SYSTEM_PROCESSOR MATCHES "x86_64")
   set(BOLT_ENABLE_RUNTIME ON)
 endif()