fix(collectives): for character

- builds with flang
- passes test suite with gfortran

src/caffeine/collective_subroutines/co_max_s.f90

@@ -23,7 +23,7 @@
 
     function reverse_alphabetize(lhs, rhs) result(last_alphabetically)
       character(len=*), intent(in) :: lhs, rhs
-      character(len=:), allocatable :: last_alphabetically
+      character(len=len(lhs)) :: last_alphabetically
       call assert(len(lhs)==len(rhs), "caf_co_max: LHS/RHS length match", lhs//" , "//rhs)
       last_alphabetically = max(lhs,rhs)
     end function

src/caffeine/collective_subroutines/co_min_s.f90

@@ -23,7 +23,7 @@
 
     function alphabetize(lhs, rhs) result(first_alphabetically)
       character(len=*), intent(in) :: lhs, rhs
-      character(len=:), allocatable :: first_alphabetically
+      character(len=len(lhs)) :: first_alphabetically
       call assert(len(lhs)==len(rhs), "prif_co_min: LHS/RHS length match", lhs//" , "//rhs)
       first_alphabetically = min(lhs,rhs)
     end function

src/caffeine/collective_subroutines/co_reduce_s.f90

@@ -50,7 +50,7 @@ function c_char_operation(lhs, rhs) result(lhs_op_rhs)
       import c_char
       implicit none
       character(kind=c_char,len=*), intent(in) :: lhs, rhs
-      character(kind=c_char,len=:), allocatable :: lhs_op_rhs
+      character(kind=c_char,len=len(lhs)) :: lhs_op_rhs
     end function
 
     pure function c_float_complex_operation(lhs, rhs) result(lhs_op_rhs)