[cmake] Add ability to customize (and skip) debugserver codesign

[labath]

Summary

This adds the ability to customize the debugserver codesign process via cmake cache variable. The
user can set the codesign indentity (with the default being the customary lldb_codesign), and if
the identity is set to a empty string, the codesign step is skipped completely.

We needed the last feature to enable building lldb on buildservers which do not have the right
certificates installed.

[tberghammer]

lgtm

[sas]

This is really useful.

lldb/trunk/tools/debugserver/source/MacOSX/CMakeLists.txt

 set_source_files_properties(
   HasAVX.s
   # Necessary since compilation will fail with stand-alone assembler
   PROPERTIES LANGUAGE C COMPILE_FLAGS "-x assembler-with-cpp"
   )
 
 target_link_libraries(debugserver ${DEBUGSERVER_USED_LIBS})
 
-# Sign the debugserver binary
-set (CODESIGN_IDENTITY lldb_codesign)
+set(LLDB_CODESIGN_IDENTITY "lldb_codesign"
+  CACHE STRING "Identity used for code signing. Set to empty string to skip the signing step.")
+if (NOT ("${LLDB_CODESIGN_IDENTITY}" STREQUAL ""))
   execute_process(
     COMMAND xcrun -f codesign_allocate
     OUTPUT_STRIP_TRAILING_WHITESPACE
     OUTPUT_VARIABLE CODESIGN_ALLOCATE
     )
   # Older cmake versions don't support "-E env".
   if (${CMAKE_MAJOR_VERSION}.${CMAKE_MINOR_VERSION} LESS 3.2)
     add_custom_command(TARGET debugserver
       POST_BUILD
       # Note: --entitlements option removed, as it causes errors when debugging.
-    # was: COMMAND CODESIGN_ALLOCATE=${CODESIGN_ALLOCATE} codesign --entitlements ${CMAKE_CURRENT_SOURCE_DIR}/../debugserver-entitlements.plist --force --sign ${CODESIGN_IDENTITY} debugserver
-    COMMAND CODESIGN_ALLOCATE=${CODESIGN_ALLOCATE} codesign --force --sign ${CODESIGN_IDENTITY} debugserver
+      # was: COMMAND CODESIGN_ALLOCATE=${CODESIGN_ALLOCATE} codesign --entitlements ${CMAKE_CURRENT_SOURCE_DIR}/../debugserver-entitlements.plist --force --sign ${LLDB_CODESIGN_IDENTITY} debugserver
+      COMMAND CODESIGN_ALLOCATE=${CODESIGN_ALLOCATE} codesign --force --sign ${LLDB_CODESIGN_IDENTITY} debugserver
       WORKING_DIRECTORY ${CMAKE_BINARY_DIR}/bin
     )
   else()
     add_custom_command(TARGET debugserver
       POST_BUILD
       # Note: --entitlements option removed (see comment above).
-    COMMAND ${CMAKE_COMMAND} -E env CODESIGN_ALLOCATE=${CODESIGN_ALLOCATE} codesign --force --sign ${CODESIGN_IDENTITY} debugserver
+      COMMAND ${CMAKE_COMMAND} -E env CODESIGN_ALLOCATE=${CODESIGN_ALLOCATE} codesign --force --sign ${LLDB_CODESIGN_IDENTITY} debugserver
       WORKING_DIRECTORY ${CMAKE_BINARY_DIR}/bin
     )
   endif()
+endif()
 
 install(TARGETS debugserver
   RUNTIME DESTINATION bin
   )