changes for clang>=21 (#20)

Author: ajaypanyala

FindStandardFortran.cmake

@@ -21,7 +21,10 @@ if(CMAKE_Fortran_COMPILER_ID MATCHES "GNU")
 elseif(CMAKE_Fortran_COMPILER_ID MATCHES "Intel")
     set(STANDARDFORTRAN_LIBS ifcore)
 elseif(CMAKE_Fortran_COMPILER_ID STREQUAL "LLVMFlang")
-    set(STANDARDFORTRAN_LIBS FortranRuntime FortranDecimal)
+  set(STANDARDFORTRAN_LIBS FortranRuntime FortranDecimal)
+  if(CMAKE_Fortran_COMPILER_VERSION VERSION_GREATER_EQUAL "21.1")
+    set(STANDARDFORTRAN_LIBS flang_rt.runtime FortranDecimal)
+  endif()
 elseif(CMAKE_Fortran_COMPILER_ID MATCHES "Flang")
     set(STANDARDFORTRAN_LIBS flang flangrti pgmath)
     #CMAKE_Fortran_COMPILER_ID does not give "ArmFlang"