[flang][OpenMP] Try to unify induction var privatization

This PR tries to unify the paths taken by flang to privatize the
induction variable of loops. With the changes introduced here, both
cases below are now privatized in the same way:

```fortran
subroutine nested_constructs
    implicit none
    integer :: i

    !$omp parallel default(private)
      do i = 1, 10
      end do
    !$omp end parallel
end subroutine
```

```fortran
subroutine nested_constructs
    implicit none
    integer :: i

    !$omp parallel private(i)
      do i = 1, 10
      end do
    !$omp end parallel
end subroutine
```

Author: ergawy

flang/lib/Semantics/resolve-directives.cpp

@@ -1674,7 +1674,6 @@ void OmpAttributeVisitor::ResolveSeqLoopIndexInParallelOrTaskConstruct(
   // parallel or task
   if (auto *symbol{ResolveOmp(iv, Symbol::Flag::OmpPrivate, targetIt->scope)}) {
     targetIt++;
-    symbol->set(Symbol::Flag::OmpPreDetermined);
     iv.symbol = symbol; // adjust the symbol within region
     for (auto it{dirContext_.rbegin()}; it != targetIt; ++it) {
       AddToContextObjectWithDSA(*symbol, Symbol::Flag::OmpPrivate, *it);

flang/test/Lower/OpenMP/default-clause.f90

@@ -537,16 +537,21 @@ subroutine nested_constructs
 
     integer :: y, z
 !CHECK: omp.parallel {
-!CHECK: %[[INNER_J:.*]] = fir.alloca i32 {bindc_name = "j", pinned}
-!CHECK: %[[INNER_J_DECL:.*]]:2 = hlfir.declare %[[INNER_J]] {{.*}}
-!CHECK: %[[INNER_I:.*]] = fir.alloca i32 {bindc_name = "i", pinned}
-!CHECK: %[[INNER_I_DECL:.*]]:2 = hlfir.declare %[[INNER_I]] {{.*}}
+
 !CHECK: %[[INNER_Y:.*]] = fir.alloca i32 {bindc_name = "y", pinned, uniq_name = "_QFnested_constructsEy"}
 !CHECK: %[[INNER_Y_DECL:.*]]:2 = hlfir.declare %[[INNER_Y]] {{.*}}
 !CHECK: %[[TEMP:.*]] = fir.load %[[Y_DECL]]#0 : !fir.ref<i32>
 !CHECK: hlfir.assign %[[TEMP]] to %[[INNER_Y_DECL]]#0 temporary_lhs : i32, !fir.ref<i32>
+
+!CHECK: %[[INNER_I:.*]] = fir.alloca i32 {bindc_name = "i", pinned, uniq_name
+!CHECK: %[[INNER_I_DECL:.*]]:2 = hlfir.declare %[[INNER_I]] {{.*}}
+
+!CHECK: %[[INNER_J:.*]] = fir.alloca i32 {bindc_name = "j", pinned, uniq_name
+!CHECK: %[[INNER_J_DECL:.*]]:2 = hlfir.declare %[[INNER_J]] {{.*}}
+
 !CHECK: %[[INNER_Z:.*]] = fir.alloca i32 {bindc_name = "z", pinned, uniq_name = "_QFnested_constructsEz"}
 !CHECK: %[[INNER_Z_DECL:.*]]:2 = hlfir.declare %[[INNER_Z]] {{.*}}
+
     !$omp parallel default(private) firstprivate(y)
 !CHECK: {{.*}} = fir.do_loop {{.*}} {
       do i = 1, 10

flang/test/Semantics/OpenMP/do05-positivecase.f90

@@ -9,7 +9,7 @@ program omp_do
   !DEF: /omp_do/n ObjectEntity INTEGER(4)
   integer i,n
   !$omp parallel
-  !DEF: /omp_do/OtherConstruct1/i (OmpPrivate, OmpPreDetermined) HostAssoc INTEGER(4)
+  !DEF: /omp_do/OtherConstruct1/i (OmpPrivate) HostAssoc INTEGER(4)
   do i=1,10
     !$omp single
     print *, "hello"

flang/test/Semantics/OpenMP/symbol08.f90

@@ -37,7 +37,7 @@ subroutine test_do
   do j=6,10
    !REF: /test_do/a
    a(1,1,1) = 0.
-   !DEF: /test_do/OtherConstruct1/k (OmpPrivate, OmpPreDetermined) HostAssoc INTEGER(4)
+   !DEF: /test_do/OtherConstruct1/k (OmpPrivate) HostAssoc INTEGER(4)
    do k=11,15
     !REF: /test_do/a
     !REF: /test_do/OtherConstruct1/k
@@ -170,9 +170,9 @@ subroutine test_simd
 !$omp parallel do simd
  !DEF: /test_simd/OtherConstruct1/i (OmpLinear, OmpPreDetermined) HostAssoc INTEGER(4)
  do i=1,5
-  !DEF: /test_simd/OtherConstruct1/j (OmpPrivate, OmpPreDetermined) HostAssoc INTEGER(4)
+  !DEF: /test_simd/OtherConstruct1/j (OmpPrivate) HostAssoc INTEGER(4)
   do j=6,10
-   !DEF: /test_simd/OtherConstruct1/k (OmpPrivate, OmpPreDetermined) HostAssoc INTEGER(4)
+   !DEF: /test_simd/OtherConstruct1/k (OmpPrivate) HostAssoc INTEGER(4)
    do k=11,15
     !REF: /test_simd/a
     !REF: /test_simd/OtherConstruct1/k
@@ -228,7 +228,7 @@ subroutine test_seq_loop
   print *, i, j
   !$omp parallel
   !REF: /test_seq_loop/i
-  !DEF: /test_seq_loop/OtherConstruct1/OtherConstruct1/j (OmpPrivate, OmpPreDetermined) HostAssoc INTEGER(4)
+  !DEF: /test_seq_loop/OtherConstruct1/OtherConstruct1/j (OmpPrivate) HostAssoc INTEGER(4)
   print *, i, j
   !$omp do
   !DEF: /test_seq_loop/OtherConstruct1/OtherConstruct1/OtherConstruct1/i (OmpPrivate, OmpPreDetermined) HostAssoc INTEGER(4)