NAG: Use -PIC for Fortran position-independent code (#13932)

The Numerical Algorithms Group (NAG) Fortran compiler documents -PIC for
position-independent code.

Modules/Compiler/NAG-Fortran.cmake

@@ -32,3 +32,4 @@ set(CMAKE_Fortran_MODDIR_FLAG "-mdir ")
 set(CMAKE_SHARED_LIBRARY_Fortran_FLAGS "-PIC")
 set(CMAKE_Fortran_FORMAT_FIXED_FLAG "-fixed")
 set(CMAKE_Fortran_FORMAT_FREE_FLAG "-free")
+set(CMAKE_Fortran_COMPILE_OPTIONS_PIC "-PIC")