Fix -pthread handling in Debian buster

FindBoost.cmake blindly adds `${CMAKE_THREAD_LIBS_INIT}` to
`${Boost_LIBRARIES}` when the component `thread` is found.
On Debian buster the `FindThreads.cmake` sets that to `-pthread`.
This breaks a bunch of stuff becakse `-pthread` is a linker flag, not a
library.

There were earlier fixes for `-lpthread`.
This PR expands upon them.
First this PR modifies the fix from ros#998 to not add `-l` to any linker flag.
Second it adds to the fix in ros#975 to make sure `-pthread` is passed to
downstream users.
There's no standard cmake variable for linker flags, so this PR opts to
create an interface target with just the flag, and add that to
`${PROJECT_NAME}_LIBRARIES` instead.

Both this PR and ros-visualization/python_qt_binding#68 are required to strip or `qt_gui_cpp` will fail at link time.

Signed-off-by: Shane Loretz <sloretz@osrfoundation.org>

cmake/catkin_package.cmake

@@ -270,7 +270,8 @@ function(_catkin_package)
   catkin_filter_libraries_for_build_configuration(libraries ${PKG_CONFIG_LIBRARIES})
   foreach(library ${libraries})
     if(NOT IS_ABSOLUTE ${library})
-      if(NOT ${library} MATCHES "^-l")
+      # Append -l to anything that's not a linker flag
+      if(NOT ${library} MATCHES "^-")
         set(library "-l${library}")
       endif()
     endif()

cmake/templates/pkgConfig.cmake.in

@@ -123,6 +123,22 @@ foreach(library ${libraries})
     list(APPEND @PROJECT_NAME@_LIBRARIES ${library})
   elseif(${library} MATCHES "^-l")
     list(APPEND @PROJECT_NAME@_LIBRARIES ${library})
+  elseif(${library} MATCHES "^-")
+    # This is a linker flag/option (like -pthread)
+    # There's no standard variable for these, so create an interface library to hold it
+    if(NOT @PROJECT_NAME@_NUM_DUMMY_TARGETS)
+        set(@PROJECT_NAME@_NUM_DUMMY_TARGETS 0)
+    endif()
+    MATH(EXPR VAR "${@PROJECT_NAME@_NUM_DUMMY_TARGETS}+1")
+    add_library("catkin::@PROJECT_NAME@::dummy${@PROJECT_NAME@_NUM_DUMMY_TARGETS}" INTERFACE IMPORTED)
+    if("${CMAKE_VERSION}" VERSION_LESS "3.13.0")
+        set_target_properties(
+          "catkin::@PROJECT_NAME@::dummy${@PROJECT_NAME@_NUM_DUMMY_TARGETS}"
+          PROPERTIES LINK_FLAGS $<TARGET_PROPERTY:LINK_FLAGS> "${library}")
+    else()
+        target_link_options("catkin::@PROJECT_NAME@::dummy${@PROJECT_NAME@_NUM_DUMMY_TARGETS}" INTERFACE "${library}")
+    endif()
+    list(APPEND @PROJECT_NAME@_LIBRARIES "catkin::@PROJECT_NAME@::dummy${@PROJECT_NAME@_NUM_DUMMY_TARGETS}")
   elseif(TARGET ${library})
     list(APPEND @PROJECT_NAME@_LIBRARIES ${library})
   elseif(IS_ABSOLUTE ${library})