deps: Build bundled dependencies automatically for IDEs

Environment variables are used to detect when the project is being built
from within Clion or Visual Studio, so that the build process can be
simplified by automatically building the bundled dependencies for them.

CMakeLists.txt

@@ -20,7 +20,34 @@ if(DEFINED ENV{DEPS_BUILD_DIR})
   set(DEPS_PREFIX "$ENV{DEPS_BUILD_DIR}/usr" CACHE PATH "Path prefix for finding dependencies")
 else()
   set(DEPS_PREFIX "${CMAKE_CURRENT_SOURCE_DIR}/.deps/usr" CACHE PATH "Path prefix for finding dependencies")
+  # When running from within CLion or Visual Studio,
+  # build bundled dependencies automatically.
+  if(NOT EXISTS ${DEPS_PREFIX}
+     AND (DEFINED ENV{CLION_IDE}
+          OR DEFINED ENV{VisualStudioEdition}))
+    message(STATUS "Building dependencies...")
+    set(DEPS_BUILD_DIR ${PROJECT_BINARY_DIR}/.deps)
+    file(MAKE_DIRECTORY ${DEPS_BUILD_DIR})
+    execute_process(
+      COMMAND ${CMAKE_COMMAND} -G ${CMAKE_GENERATOR}
+        -DCMAKE_TOOLCHAIN_FILE=${CMAKE_TOOLCHAIN_FILE}
+        -DCMAKE_BUILD_TYPE=${CMAKE_BUILD_TYPE}
+        -DCMAKE_C_COMPILER=${CMAKE_C_COMPILER}
+        -DCMAKE_C_FLAGS=${CMAKE_C_FLAGS}
+        -DCMAKE_C_FLAGS_DEBUG=${CMAKE_C_FLAGS_DEBUG}
+        -DCMAKE_C_FLAGS_MINSIZEREL=${CMAKE_C_FLAGS_MINSIZEREL}
+        -DCMAKE_C_FLAGS_RELWITHDEBINFO=${CMAKE_C_FLAGS_RELWITHDEBINFO}
+        -DCMAKE_C_FLAGS_RELEASE=${CMAKE_C_FLAGS_RELEASE}
+        -DCMAKE_MAKE_PROGRAM=${CMAKE_MAKE_PROGRAM}
+        ${PROJECT_SOURCE_DIR}/third-party
+      WORKING_DIRECTORY ${DEPS_BUILD_DIR})
+    execute_process(
+      COMMAND ${CMAKE_COMMAND} --build ${DEPS_BUILD_DIR}
+        --config ${CMAKE_BUILD_TYPE})
+    set(DEPS_PREFIX ${DEPS_BUILD_DIR}/usr)
+  endif()
 endif()
+
 if(CMAKE_CROSSCOMPILING AND NOT UNIX)
   list(INSERT CMAKE_FIND_ROOT_PATH 0 ${DEPS_PREFIX})
   list(INSERT CMAKE_PREFIX_PATH 0 ${DEPS_PREFIX}/../host/bin)