[CMake] fix runpath for ELF platforms

Remove the absolute path to the host stdlib for libswiftDispatch.so and add $ORIGIN
to it and libdispatch.so.

Author: finagolfin

src/CMakeLists.txt

@@ -155,6 +155,10 @@ if(CMAKE_SYSTEM_NAME STREQUAL Darwin)
     "-Xlinker -alias_list -Xlinker ${PROJECT_SOURCE_DIR}/xcodeconfig/libdispatch.aliases")
 endif()
 
+if(NOT CMAKE_SYSTEM_NAME MATCHES "Darwin|Windows")
+  set_target_properties(dispatch PROPERTIES INSTALL_RPATH "$ORIGIN")
+endif()
+
 if(ENABLE_SWIFT)
   add_subdirectory(swift)
 endif()

src/swift/CMakeLists.txt

@@ -59,4 +59,7 @@ if(NOT BUILD_SHARED_LIBS)
   install(TARGETS DispatchStubs
     EXPORT dispatchExports
     DESTINATION ${INSTALL_TARGET_DIR})
+elseif(NOT CMAKE_SYSTEM_NAME MATCHES "Darwin|Windows")
+  target_link_options(swiftDispatch PRIVATE "SHELL:-no-toolchain-stdlib-rpath")
+  set_target_properties(swiftDispatch PROPERTIES INSTALL_RPATH "$ORIGIN")
 endif()