[NFC][SYCL] Fix test to properly pick up device libraries (#13913)

The sycl-offload-intelfpga.cpp test was recently modified to check that
the proper device library objects are picked up. The test was not using
the local testing sysroot to pick up the files, causing problems when
the actual libraries are not built with the compiler before the test is
run.

Author: mdtoguchi

clang/test/Driver/sycl-offload-intelfpga.cpp

@@ -271,9 +271,11 @@
 
 // When using -fintelfpga, we unbundle the device libraries instead of using
 // the LLVM-IR .bc files.
-// RUN: %clangxx -fintelfpga -ccc-print-phases %s 2>&1 \
+// RUN: %clangxx -fintelfpga -ccc-print-phases \
+// RUN:          --sysroot=%S/Inputs/SYCL %s 2>&1 \
 // RUN:  | FileCheck -check-prefix UNBUNDLE_DEVICELIB %s
-// RUN: %clangxx -fsycl -fsycl-targets=spir64_fpga -ccc-print-phases %s 2>&1 \
+// RUN: %clangxx -fsycl -fsycl-targets=spir64_fpga -ccc-print-phases \
+// RUN:          --sysroot=%S/Inputs/SYCL %s 2>&1 \
 // RUN:  | FileCheck -check-prefix UNBUNDLE_DEVICELIB %s
 // UNBUNDLE_DEVICELIB: [[#DEVLIB:]]: input, "{{.*}}libsycl-itt-user-wrappers{{.*}}", object
 // UNBUNDLE_DEVICELIB: [[#DEVLIB+1]]: clang-offload-unbundler, {[[#DEVLIB]]}, object