build: link libraries by full path (for luv.so) (#10661)

Use "luv" as imported library to work around "-lluv" being used due to
missing SONAME.

Fixes https://github.com/neovim/neovim/issues/10407.
Ref: https://gitlab.kitware.com/cmake/cmake/issues/19578
Ref: https://github.com/NixOS/nixpkgs/issues/64400#issuecomment-516557253

cmake/FindLibLUV.cmake

@@ -14,7 +14,8 @@ set(LIBLUV_DEFINITIONS ${PC_LIBLUV_CFLAGS_OTHER})
 find_path(LIBLUV_INCLUDE_DIR luv/luv.h
           PATHS ${PC_LIBLUV_INCLUDEDIR} ${PC_LIBLUV_INCLUDE_DIRS})
 
-list(APPEND LIBLUV_NAMES luv)
+# Explicitly look for luv.so. #10407
+list(APPEND LIBLUV_NAMES luv luv${CMAKE_SHARED_LIBRARY_SUFFIX})
 
 find_library(LIBLUV_LIBRARY NAMES ${LIBLUV_NAMES}
   HINTS ${PC_LIBLUV_LIBDIR} ${PC_LIBLUV_LIBRARY_DIRS})

src/nvim/CMakeLists.txt

@@ -381,9 +381,14 @@ if(WIN32)
   list(APPEND NVIM_LINK_LIBRARIES ${WINPTY_LIBRARIES})
 endif()
 
+# Use "luv" as imported library, to work around CMake using "-lluv" for
+# "luv.so".  #10407
+add_library(luv UNKNOWN IMPORTED)
+set_property(TARGET luv PROPERTY IMPORTED_LOCATION ${LIBLUV_LIBRARIES})
+
 # Put these last on the link line, since multiple things may depend on them.
 list(APPEND NVIM_LINK_LIBRARIES
-  ${LIBLUV_LIBRARIES}
+  luv
   ${LIBUV_LIBRARIES}
   ${MSGPACK_LIBRARIES}
   ${LIBVTERM_LIBRARIES}
@@ -401,6 +406,7 @@ endif()
 
 set(NVIM_EXEC_LINK_LIBRARIES ${NVIM_LINK_LIBRARIES} ${LUA_PREFERRED_LIBRARIES})
 
+# Add IPO flags (for LTO), or error if CMake does not know the flags. #8654
 if(POLICY CMP0069)
   cmake_policy(SET CMP0069 NEW)
 endif()