[Libomptarget] Fix test logic for optionally adding the libcgpu.a

Summary:
This was not operating as expected and was causing the build to fail on
non-configured systems.

Author: jhuber6

openmp/libomptarget/test/lit.cfg

@@ -216,12 +216,12 @@ for libomptarget_target in config.libomptarget_all_targets:
             "%libomptarget-run-" + libomptarget_target))
         config.substitutions.append(("%libomptarget-compilexx-" + \
             libomptarget_target, \
-            "%clangxx-" + libomptarget_target + " %s -o %t" \
-            " -lcgpu" if config.libomptarget_has_libc else ""))
+            "%clangxx-" + libomptarget_target + " %s -o %t" + \
+            (" -lcgpu" if config.libomptarget_has_libc else "")))
         config.substitutions.append(("%libomptarget-compile-" + \
             libomptarget_target, \
-            "%clang-" + libomptarget_target + " %s -o %t"
-            " -lcgpu" if config.libomptarget_has_libc else ""))
+            "%clang-" + libomptarget_target + " %s -o %t" +
+            (" -lcgpu" if config.libomptarget_has_libc else "")))
         config.substitutions.append(("%libomptarget-compileoptxx-run-and-check-" + \
             libomptarget_target, \
             "%libomptarget-compileoptxx-and-run-" + libomptarget_target + \
@@ -240,12 +240,12 @@ for libomptarget_target in config.libomptarget_all_targets:
             "%libomptarget-run-" + libomptarget_target))
         config.substitutions.append(("%libomptarget-compileoptxx-" + \
             libomptarget_target, \
-            "%clangxx-" + libomptarget_target + " -O3 %s -o %t"
-            " -lcgpu" if config.libomptarget_has_libc else ""))
+            "%clangxx-" + libomptarget_target + " -O3 %s -o %t" +
+            (" -lcgpu" if config.libomptarget_has_libc else "")))
         config.substitutions.append(("%libomptarget-compileopt-" + \
             libomptarget_target, \
-            "%clang-" + libomptarget_target + " -O3 %s -o %t"
-            " -lcgpu" if config.libomptarget_has_libc else ""))
+            "%clang-" + libomptarget_target + " -O3 %s -o %t" +
+            (" -lcgpu" if config.libomptarget_has_libc else "")))
         config.substitutions.append(("%libomptarget-run-" + \
             libomptarget_target, \
             "%t"))