perf symbols: Provide a GElf_Nhdr typedef

This one can be safely defined to be Elf64_Nhdr, as it is in elfutils's
libelf, but not on musl libc, as both Elf64_Nhdr and  Elf32_Nhdr have
the same layout.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-w8z8614l03lc8bip4ijbywbt@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/symbol-elf.c

@@ -16,6 +16,7 @@
 #define EM_AARCH64	183  /* ARM 64 bit */
 #endif
 
+typedef Elf64_Nhdr GElf_Nhdr;
 
 #ifdef HAVE_CPLUS_DEMANGLE_SUPPORT
 extern char *cplus_demangle(const char *, int);