RISC-V: Fix target-attr-norelax.c testcase

The target-attr-norelax.c testcase was failing due to the redundant "\t"
check in the assembly output, and forgot to skip the check for lto build
in the testcase.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/target-attr-norelax.c: Fix testcase.