Add -lm to plugin.cmake for Linux

TracePluginCustomCmake uses plugin.cmake which also needs libm.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: lsk567

plugin.cmake

@@ -85,6 +85,9 @@ if(APPLE)
 elseif(UNIX)
     target_link_libraries(${LF_MAIN_TARGET} PRIVATE "-lstdc++")
     message(STATUS "Linked C++ standard library (libstdc++)")
+    # Math library (gRPC uses lround, etc.)
+    target_link_libraries(${LF_MAIN_TARGET} PRIVATE "-lm")
+    message(STATUS "Linked math library (libm)")
 endif()
 
 # Link CoreFoundation framework (required by Abseil on macOS for time zone handling)