[RISCV][NFC] s/riscv32-linux-unknown-elf/riscv32-unknown-linux-gnu in test/Driver/riscv32-toolchain.c
[RISCV][NFC] s/riscv32-linux-unknown-elf/riscv32-unknown-linux-gnu in test/Driver/riscv32-toolchain.c

riscv32-linux-unknown-elf was a weird thing to test for as it doesn't match
the triple used in any common RISC-V toolchain distributions (e.g.
riscv-gnu-toolchain scripts produce riscv{32,64}-unknown-linux-gnu).



git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@357693 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang