[OpenMP] Enable position independent code for libomptarget

Summary:
This option used to be passed manually by the `-fPIC` option that was
always enabled by the LLVM flags. Since we now do this manually we want
to specify that these are supposed for use fPIC code.

openmp/libomptarget/plugins-nextgen/CMakeLists.txt

@@ -70,6 +70,7 @@ if(CMAKE_SYSTEM_PROCESSOR MATCHES "${tmachine}$")
       LIBRARY DESTINATION "${OPENMP_INSTALL_LIBDIR}")
     set_target_properties("omptarget.rtl.${tmachine_libname}" PROPERTIES
       INSTALL_RPATH "$ORIGIN" BUILD_RPATH "$ORIGIN:${CMAKE_CURRENT_BINARY_DIR}/.."
+      POSITION_INDEPENDENT_CODE ON
       CXX_VISIBILITY_PRESET protected)
 
     target_include_directories( "omptarget.rtl.${tmachine_libname}" PRIVATE

openmp/libomptarget/src/CMakeLists.txt

@@ -46,5 +46,8 @@ endif()
 
 # libomptarget.so needs to be aware of where the plugins live as they
 # are now separated in the build directory.
-set_target_properties(omptarget PROPERTIES INSTALL_RPATH "$ORIGIN" BUILD_RPATH "$ORIGIN:${CMAKE_CURRENT_BINARY_DIR}/..")
+set_target_properties(omptarget PROPERTIES
+                      POSITION_INDEPENDENT_CODE ON
+                      INSTALL_RPATH "$ORIGIN"
+                      BUILD_RPATH "$ORIGIN:${CMAKE_CURRENT_BINARY_DIR}/..")
 install(TARGETS omptarget LIBRARY COMPONENT omptarget DESTINATION "${OPENMP_INSTALL_LIBDIR}")