Revert "[Flang][OpenMP] Disable declarate target tests on Windows" (#77324)

Reverts #77306

These tests aren't broken on Windows, marking them XFAIL will just ~
consistently fail the build.

Author: joker-eph

flang/test/Lower/OpenMP/FIR/declare-target-implicit-func-and-subr-cap-enter.f90

@@ -3,8 +3,6 @@
 !RUN: bbc -emit-fir -fopenmp %s -o - | FileCheck %s
 !RUN: bbc -emit-fir -fopenmp -fopenmp-is-target-device %s -o - | FileCheck %s --check-prefix=DEVICE
 
-!XFAIL: system-windows
-
 ! CHECK-LABEL: func.func @_QPimplicitly_captured_twice
 ! CHECK-SAME: {{.*}}attributes {omp.declare_target = #omp.declaretarget<device_type = (any), capture_clause = (enter)>{{.*}}}
 function implicitly_captured_twice() result(k)

flang/test/Lower/OpenMP/FIR/declare-target-implicit-func-and-subr-cap.f90

@@ -3,8 +3,6 @@
 !RUN: bbc -emit-fir -fopenmp %s -o - | FileCheck %s
 !RUN: bbc -emit-fir -fopenmp -fopenmp-is-target-device %s -o - | FileCheck %s --check-prefix=DEVICE
 
-!XFAIL: system-windows
-
 ! CHECK-LABEL: func.func @_QPimplicitly_captured
 ! CHECK-SAME: {{.*}}attributes {omp.declare_target = #omp.declaretarget<device_type = (any), capture_clause = (to)>{{.*}}}
 function implicitly_captured(toggle) result(k)

flang/test/Lower/OpenMP/declare-target-implicit-func-and-subr-cap-enter.f90

@@ -3,8 +3,6 @@
 !RUN: bbc -emit-hlfir -fopenmp %s -o - | FileCheck %s
 !RUN: bbc -emit-hlfir -fopenmp -fopenmp-is-target-device %s -o - | FileCheck %s --check-prefix=DEVICE
 
-!XFAIL: system-windows
-
 ! CHECK-LABEL: func.func @_QPimplicitly_captured_twice
 ! CHECK-SAME: {{.*}}attributes {omp.declare_target = #omp.declaretarget<device_type = (any), capture_clause = (enter)>{{.*}}}
 function implicitly_captured_twice() result(k)

flang/test/Lower/OpenMP/declare-target-implicit-func-and-subr-cap.f90

@@ -3,8 +3,6 @@
 !RUN: bbc -emit-hlfir -fopenmp %s -o - | FileCheck %s
 !RUN: bbc -emit-hlfir -fopenmp -fopenmp-is-target-device %s -o - | FileCheck %s --check-prefix=DEVICE
 
-!XFAIL: system-windows
-
 ! CHECK-LABEL: func.func @_QPimplicitly_captured
 ! CHECK-SAME: {{.*}}attributes {omp.declare_target = #omp.declaretarget<device_type = (any), capture_clause = (to)>{{.*}}}
 function implicitly_captured(toggle) result(k)