Only include externals when actually needed

This adds an option to use the system library for HIDAPI if enabled, and
gates the misc and regex external libraries to only the platforms where
they're actually needed.

Author: davide125

Diff for: CMakeLists.txt

@@ -14,6 +14,7 @@ option(FORCE_SSE "Compile with SSE instruction only" ON)
 option(FORCE_SSSE3 "Compile with SSSE3 instruction only" OFF)
 option(FORCE_SSE41 "Compile with SSE4.1 instruction only" OFF)
 option(OPTIONAL_TEST "Compile optional test (might be broken)" OFF)
+option(USE_SYSTEM_HIDAPI "Use the system library for hidapi" OFF)
 # UNITTEST option must be after CMAKE_BUILT_TYPE
 
 # where cmake find custom modules
@@ -72,7 +73,11 @@ set(CUSTOM_SRC_DIR "${CMAKE_SOURCE_DIR}/src")
 set(CUSTOM_EXTERNAL_DIR "${CMAKE_SOURCE_DIR}/external")
 set(CUSTOM_MISC_DIR "${CUSTOM_EXTERNAL_DIR}/misc")
 set(CUSTOM_REGEX_DIR "${CUSTOM_EXTERNAL_DIR}/regex")
-set(CUSTOM_HIDAPI_DIR "${CUSTOM_EXTERNAL_DIR}/hidapi")
+if(USE_SYSTEM_HIDAPI)
+  find_package(hidapi REQUIRED)
+else()
+  set(CUSTOM_HIDAPI_DIR "${CUSTOM_EXTERNAL_DIR}/hidapi")
+endif()
 set(CUSTOM_GEOTRANZ_DIR "${CUSTOM_EXTERNAL_DIR}/geotranz")
 set(CUSTOM_DATA_DIR "${CMAKE_SOURCE_DIR}/data")
 set(CUSTOM_SCRIPTS_DIR "${CMAKE_SOURCE_DIR}/scripts")
@@ -374,9 +379,15 @@ add_subdirectory(data)
 
 # external libraries
 add_subdirectory(${CUSTOM_GEOTRANZ_DIR})
-add_subdirectory(${CUSTOM_REGEX_DIR})
-add_subdirectory(${CUSTOM_HIDAPI_DIR})
-add_subdirectory(${CUSTOM_MISC_DIR})
+if(WIN32)
+  add_subdirectory(${CUSTOM_REGEX_DIR})
+endif()
+if(NOT USE_SYSTEM_HIDAPI)
+  add_subdirectory(${CUSTOM_HIDAPI_DIR})
+endif()
+if(NOT LINUX)
+  add_subdirectory(${CUSTOM_MISC_DIR})
+endif()
 
 # direwolf source code and utilities
 add_subdirectory(src)