[test][flang][driver] Fix test that assumes libomp default (llvm#119368)

This patch supplements the fix introduced by PR llvm#119319.

Author: pawosm-arm

flang/test/Driver/config-file.f90

@@ -64,9 +64,9 @@
 
 !--- The linker input flags should be moved to the end of input list and appear only when linking.
 ! RUN: %flang --target=aarch64-unknown-linux-gnu --config %S/Inputs/config-l.cfg %s -lmylib -Wl,foo.a -### 2>&1 | FileCheck %s -check-prefix CHECK-LINKING
-! RUN: %flang --target=aarch64-unknown-linux-gnu --config %S/Inputs/config-l.cfg -fopenmp %s -lmylib -Wl,foo.a -### 2>&1 | FileCheck %s -check-prefix CHECK-LINKING-LIBOMP-GOES-AFTER
+! RUN: %flang --target=aarch64-unknown-linux-gnu --config %S/Inputs/config-l.cfg -fopenmp=libomp %s -lmylib -Wl,foo.a -### 2>&1 | FileCheck %s -check-prefix CHECK-LINKING-LIBOMP-GOES-AFTER
 ! RUN: %flang --target=aarch64-unknown-linux-gnu --config %S/Inputs/config-l.cfg -S %s -### 2>&1 | FileCheck %s -check-prefix CHECK-NOLINKING
-! RUN: %flang --target=aarch64-unknown-linux-gnu --config %S/Inputs/config-l.cfg -fopenmp -S %s -### 2>&1 | FileCheck %s -check-prefix CHECK-NOLINKING-OPENMP
+! RUN: %flang --target=aarch64-unknown-linux-gnu --config %S/Inputs/config-l.cfg -fopenmp=libomp -S %s -### 2>&1 | FileCheck %s -check-prefix CHECK-NOLINKING-OPENMP
 ! RUN: %flang --target=x86_64-pc-windows-msvc    --config %S/Inputs/config-l.cfg %s -lmylib -Wl,foo.lib -### 2>&1 | FileCheck %s -check-prefix CHECK-LINKING-MSVC
 ! RUN: %flang --target=x86_64-pc-windows-msvc    --config %S/Inputs/config-l.cfg -S %s -### 2>&1 | FileCheck %s -check-prefix CHECK-NOLINKING-MSVC
 ! CHECK-LINKING: Configuration file: {{.*}}Inputs{{.}}config-l.cfg