linuxPackages_*.perf: Fix build after kernel 4.1

In 4.1, the build system changed, and it now wants to execute ld like this:

ld -r -o util/scripting-engines/libperf-in.o util/scripting-engines/trace-event-perl.o util/scripting-engines/trace-event-python.o

The actual problem seems to be that `buildInputs = [elfutils ...]`
causes 'ld' to point to elfutils in PATH instead of the usual binutils.

So remove elfutils from buildInputs and set NIX_CFLAGS_* manually. This
is a slight hack, but there is some precedent:
0761f81da7/pkgs/tools/package-management/rpm/default.nix (L13)

Fixes #9095.

pkgs/os-specific/linux/kernel/perf.nix

@@ -23,10 +23,13 @@ stdenv.mkDerivation {
   # perf refers both to newt and slang
   # binutils is required for libbfd.
   nativeBuildInputs = [ asciidoc xmlto docbook_xsl docbook_xml_dtd_45 libxslt flex bison ];
-  buildInputs = [ elfutils python perl newt slang pkgconfig libunwind binutils ] ++
+  buildInputs = [ python perl newt slang pkgconfig libunwind binutils ] ++
     stdenv.lib.optional withGtk gtk;
 
-  NIX_CFLAGS_COMPILE = "-Wno-error=cpp";
+  # Note: we don't add elfutils to buildInputs, since it provides a
+  # bad `ld' and other stuff.
+  NIX_CFLAGS_COMPILE = "-I${elfutils}/include -Wno-error=cpp";
+  NIX_CFLAGS_LINK = "-L${elfutils}/lib";
 
   installFlags = "install install-man ASCIIDOC8=1";