perf tests clang: Fix function name for clang IR test

As stated in tests/llvm-src-base.c, the name of the bpf function should
be "bpf_func__SyS_epoll_pwait" but this clang test fails as it tries to
lookup "bpf_func__SyS_epoll_wait".

Before applying patch:

55: builtin clang support :
55.1: builtin clang compile C source to IR : FAILED!
55.2: builtin clang compile C source to ELF object : Skip

After applying patch:

55: builtin clang support :
55.1: builtin clang compile C source to IR : Ok
55.2: builtin clang compile C source to ELF object : Ok

Signed-off-by: Sandipan Das <[e-mail]>
Tested-by: Arnaldo Carvalho de Melo <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Naveen N. Rao <[e-mail]>
Fixes: e67d52d411c3 ("perf clang: Update test case to use real BPF script")
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/util/c++/clang-test.cpp

···
 	if (!M)
 		return -1;
 	for (llvm::Function& F : *M)
-		if (F.getName() == "bpf_func__SyS_epoll_wait")
+		if (F.getName() == "bpf_func__SyS_epoll_pwait")
 			return 0;
 	return -1;
 }