[flang][Driver] Guard check for pic/pie settings without driver flags (llvm#143530)

The default relocation model for clang depends on the cmake flag
CLANG_DEFAULT_PIE_ON_LINUX. By default it is set to ON, but when it's
OFF, the default relocation model will be "static".
The outcome of the test running clang without any PIC/PIE flags will
depend on the cmake flag, so make sure it only runs when the flag is ON.

Author: kparzysz

flang/test/Driver/pic-flags.f90

@@ -1,6 +1,6 @@
 ! RUN: %if aarch64-registered-target %{ %flang -v -S -emit-llvm -o - %s --target=aarch64-linux-gnu -fno-pie 2>&1 | FileCheck %s --check-prefixes=CHECK,CHECK-STATIC,CHECK-STATIC-IR %}
 
-! RUN: %if aarch64-registered-target %{ %flang -v -S -emit-llvm -o - %s --target=aarch64-linux-gnu 2>&1 | FileCheck %s --check-prefixes=CHECK,CHECK-PIE-LEVEL2,CHECK-PIE-LEVEL2-IR %}
+! RUN: %if aarch64-registered-target && clang_default_pie_on_linux %{ %flang -v -S -emit-llvm -o - %s --target=aarch64-linux-gnu 2>&1 | FileCheck %s --check-prefixes=CHECK,CHECK-PIE-LEVEL2,CHECK-PIE-LEVEL2-IR %}
 ! RUN: %if aarch64-registered-target %{ %flang -v -S -emit-llvm -o - %s --target=aarch64-linux-gnu -fpie 2>&1 | FileCheck %s --check-prefixes=CHECK,CHECK-PIE-LEVEL1,CHECK-PIE-LEVEL1-IR %}
 ! RUN: %if aarch64-registered-target %{ %flang -v -S -emit-llvm -o - %s --target=aarch64-linux-gnu -fPIE 2>&1 | FileCheck %s --check-prefixes=CHECK,CHECK-PIE-LEVEL2,CHECK-PIE-LEVEL2-IR %}