Mark dummy includes for IWYU.

Author: joto

CMakeLists.txt

@@ -408,7 +408,7 @@ if(BUILD_HEADERS)
         # Create a dummy .cpp file that includes the header file we want to
         # check.
         set(DUMMYCPP ${CMAKE_BINARY_DIR}/header_check/${libname}.cpp)
-        file(WRITE ${DUMMYCPP} "#include <${hpp}>\n")
+        file(WRITE ${DUMMYCPP} "#include <${hpp}> // IWYU pragma: keep\n")
 
         # There is no way in CMake to just compile but not link a C++ file,
         # so we pretend to build a library here.

osmium.imp

@@ -2,7 +2,7 @@
 #
 #  Configuration for Include-What-You-Use tool
 #
-#  http://include-what-you-use.org/
+#  https://include-what-you-use.org/
 #
 #-----------------------------------------------------------------------------
 [