Replace deprecated %T in 2 tests.
- Replace %T with %t as former is deprecated.
- Add an explicit --sysroot argument in a test.
Some tests were failing when gcc-10-riscv64-linux-gnu is installed on test machine.
This was happening because the test was checking a case when --gcc-toolchain is not
provided. But if --sysroot was also not provided then code could pick a toolchain
installed in /usr. So to make the test more robust, I have provided an explicit --sysroot
argument. Its value has been chosen to match the existing patterns.
Reviewed By: MaskRay
Differential Revision: https://reviews.llvm.org/D93023