cmake: add flags to use system-provided libraries

CMakeLists.txt

@@ -14,6 +14,11 @@ project(drjit-core
 #  Optional features available to users
 # ----------------------------------------------------------
 
+option(DRJIT_USE_SYSTEM_NANOTHREAD "Use the system nanothread library?" OFF)
+option(DRJIT_USE_SYSTEM_LZ4 "Use the system lz4 library?" OFF)
+option(DRJIT_USE_SYSTEM_XXHASH "Use the system xxHash library?" OFF)
+option(DRJIT_USE_SYSTEM_TSL_ROBIN_MAP "Use the system tsl-robin-map library?" OFF)
+
 option(DRJIT_DYNAMIC_LLVM "Resolve LLVM dynamically at run time?" ON)
 option(DRJIT_ENABLE_TESTS "Build Dr.Jit-Core test suite?" OFF)
 
@@ -43,6 +48,11 @@ include(ext/nanothread/ext/cmake-defaults/CMakeLists.txt)
 #  Print a few messages explaining what will be compiled
 # ----------------------------------------------------------
 
+message(STATUS "Dr.Jit-Core: using system nanothread: ${DRJIT_USE_SYSTEM_NANOTHREAD}")
+message(STATUS "Dr.Jit-Core: using system lz4: ${DRJIT_USE_SYSTEM_LZ4}")
+message(STATUS "Dr.Jit-Core: using system xxHash: ${DRJIT_USE_SYSTEM_XXHASH}")
+message(STATUS "Dr.Jit-Core: using system tsl-robin-map: ${DRJIT_USE_SYSTEM_TSL_ROBIN_MAP}")
+
 if (DRJIT_DYNAMIC_LLVM)
   message(STATUS "Dr.Jit-Core: LLVM will be loaded dynamically at runtime.")
 else()
@@ -73,32 +83,33 @@ endif()
 #  Find or build the dependencies
 # ----------------------------------------------------------
 
-find_package(nanothread)
-if (NOT nanothread_FOUND)
+if (DRJIT_USE_SYSTEM_NANOTHREAD)
+  find_package(nanothread REQUIRED)
+else()
   add_subdirectory(ext/nanothread)
   mark_as_advanced(NANOTHREAD_ENABLE_TESTS)
 endif()
 
-find_package(PkgConfig)
-if (PkgConfig_FOUND)
+if (DRJIT_USE_SYSTEM_LZ4)
+  find_package(PkgConfig REQUIRED)
   pkg_check_modules(lz4 liblz4 IMPORTED_TARGET)
   add_library(lz4 ALIAS PkgConfig::lz4)
-endif()
-if(NOT lz4_FOUND)
+else()
   add_library(lz4 ext/lz4/lz4.c)
   target_include_directories(lz4 PUBLIC ext/lz4)
 endif()
 
-find_package(xxHash)
-if (NOT xxHash_FOUND)
+if (DRJIT_USE_SYSTEM_XXHASH)
+  find_package(xxHash REQUIRED)
+else()
   add_library(xxhash ext/lz4/xxhash.c)
   target_include_directories(xxhash PUBLIC ext/lz4)
-
   add_library(xxHash::xxhash ALIAS xxhash)
 endif()
 
-find_package(tsl-robin-map)
-if (NOT tsl-robin-map_FOUND)
+if (DRJIT_USE_SYSTEM_TSL_ROBIN_MAP)
+  find_package(tsl-robin-map REQUIRED)
+else()
   add_subdirectory(ext/robin_map)
 endif()