Add an installed CMake config. (#370)

* Add an installed CMake config.

Does not perform transitive link to boringssl though.

* Install vc_compat.h header

CMakeLists.txt

@@ -336,3 +336,11 @@ INSTALL(FILES
     include/lsxpack_header.h
     DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}/lsquic
 )
+
+if(WIN32)
+    # The other file in wincompat is not used in installed headers
+    INSTALL(FILES
+        wincompat/vc_compat.h
+        DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}/lsquic
+    )
+endif()

src/liblsquic/CMakeLists.txt

@@ -130,9 +130,28 @@ ELSE()
   add_library(lsquic STATIC ${lsquic_STAT_SRCS})
 ENDIF()
 
+target_include_directories(
+    lsquic PUBLIC $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}/lsquic>)
+
 install(TARGETS lsquic
     EXPORT lsquic-targets
     LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
     ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR}
 )
 
+include(CMakePackageConfigHelpers)
+configure_package_config_file(
+    lsquic-config.cmake ${CMAKE_CURRENT_BINARY_DIR}/lsquic-config.cmake
+    INSTALL_DESTINATION share/lsquic
+    NO_CHECK_REQUIRED_COMPONENTS_MACRO
+    PATH_VARS CMAKE_INSTALL_INCLUDEDIR)
+
+install(
+    FILES ${CMAKE_CURRENT_BINARY_DIR}/lsquic-config.cmake
+    DESTINATION share/lsquic)
+
+install(
+    EXPORT lsquic-targets
+    DESTINATION share/lsquic
+    NAMESPACE lsquic::
+    FILE lsquic-targets.cmake)

src/liblsquic/lsquic-config.cmake

@@ -0,0 +1,4 @@
+@PACKAGE_INIT@
+
+set_and_check(lsquic_INCLUDE_DIR "@PACKAGE_CMAKE_INSTALL_INCLUDEDIR@")
+include("${CMAKE_CURRENT_LIST_DIR}/lsquic-targets.cmake")