Do not install vendored lib.

Index: rts/lib/CMakeLists.txt
--- rts/lib/CMakeLists.txt.orig
+++ rts/lib/CMakeLists.txt
@@ -65,7 +65,7 @@ SET(GFLAGS_INSTALL_STATIC_LIBS        FALSE)
 if (WIN32)
 	remove_definitions(-DUNICODE -D_UNICODE)
 endif()
-ADD_SUBDIRECTORY(gflags)
+ADD_SUBDIRECTORY(gflags EXCLUDE_FROM_ALL)
 if (WIN32)
 	add_definitions(-DUNICODE -D_UNICODE)
 endif()
@@ -125,13 +125,13 @@ endif()
 
 set(SIMDJSON_ENABLE_THREADS     OFF CACHE BOOL "forced by Recoil build env" FORCE)
 set(SIMDJSON_EXCEPTIONS     ON CACHE BOOL "forced by Recoil build env" FORCE)
-ADD_SUBDIRECTORY(simdjson)
+ADD_SUBDIRECTORY(simdjson EXCLUDE_FROM_ALL)
 
 # fastgltf
 set(FASTGLTF_COMPILE_AS_CPP20 ON CACHE BOOL "forced by Recoil build env" FORCE)
 set(FASTGLTF_USE_64BIT_FLOAT OFF CACHE BOOL "forced by Recoil build env" FORCE)
 set(FASTGLTF_USE_CUSTOM_SMALLVECTOR OFF CACHE BOOL "forced by Recoil build env" FORCE)
-ADD_SUBDIRECTORY(fastgltf)
+ADD_SUBDIRECTORY(fastgltf EXCLUDE_FROM_ALL)
 
 ADD_SUBDIRECTORY(squish)
 ADD_SUBDIRECTORY(rg-etc1)
@@ -147,7 +147,7 @@ option(TRACY_ON_DEMAND "Enable tracy profiling" ON)
 # raw malloc have to be used with care.
 option(TRACY_PROFILE_MEMORY "Profile memory allocations" OFF)
 
-add_subdirectory(tracy)
+add_subdirectory(tracy EXCLUDE_FROM_ALL)
 
 if (TRACY_ENABLE)
 	option(RMLUI_TRACY_PROFILING "Enable RmlUi profiling with Tracy." ON)
@@ -168,7 +168,7 @@ find_package_static(Freetype 2.8.1 REQUIRED)
 string(REPLACE "-fsingle-precision-constant" "" NEW_CMAKE_FLAGS ${CMAKE_CXX_FLAGS})
 set(SAVED_CMAKE_FLAGS ${CMAKE_CXX_FLAGS})
 set(CMAKE_CXX_FLAGS ${NEW_CMAKE_FLAGS})
-add_subdirectory(lunasvg)
+add_subdirectory(lunasvg EXCLUDE_FROM_ALL)
 set(CMAKE_CXX_FLAGS ${SAVED_CMAKE_FLAGS})
 
-add_subdirectory(RmlUi)
+add_subdirectory(RmlUi EXCLUDE_FROM_ALL)
