[tcp] link third_party TCPlp module in CMake build (#6925)

This commit changes the Makefiles so that the TCPlp module is linked
in to the code when building OpenThread using CMake. This is necessary
when script/build or script/cmake-build is used to build OpenThread.

src/core/ftd.cmake

@@ -43,5 +43,6 @@ target_sources(openthread-ftd PRIVATE ${COMMON_SOURCES})
 target_link_libraries(openthread-ftd
     PRIVATE
         ${OT_MBEDTLS}
+        tcplp
         ot-config
 )

src/core/mtd.cmake

@@ -43,5 +43,6 @@ target_sources(openthread-mtd PRIVATE ${COMMON_SOURCES})
 target_link_libraries(openthread-mtd
     PRIVATE
         ${OT_MBEDTLS}
+        tcplp
         ot-config
 )

third_party/tcplp/CMakeLists.txt

@@ -44,3 +44,21 @@ target_include_directories(${tcplp_static_target}
         ${OT_PUBLIC_INCLUDES}
         $<TARGET_PROPERTY:ot-config,INTERFACE_INCLUDE_DIRECTORIES>
 )
+
+# TCPlp calls functions that are defined by the core OpenThread (like
+# "otMessageWrite()"), so we need to add the core library (FTD or MTD, as
+# appropriate) as a link dependency.
+
+if(OT_FTD)
+    target_link_libraries(${tcplp_static_target}
+        PRIVATE
+            openthread-ftd
+    )
+endif()
+
+if(OT_MTD)
+    target_link_libraries(${tcplp_static_target}
+        PRIVATE
+            openthread-mtd
+    )
+endif()