Replaced glibc version of elf.h with musl version of elf.h.

src/third_party/musl/README

+
+    musl libc
+
+musl, pronounced like the word "mussel", is an MIT-licensed
+implementation of the standard C library targetting the Linux syscall
+API, suitable for use in a wide range of deployment environments. musl
+offers efficient static and dynamic linking support, lightweight code
+and low runtime overhead, strong fail-safe guarantees under correct
+usage, and correctness in the sense of standards conformance and
+safety. musl is built on the principle that these goals are best
+achieved through simple code that is easy to understand and maintain.
+
+The 1.1 release series for musl features coverage for all interfaces
+defined in ISO C99 and POSIX 2008 base, along with a number of
+non-standardized interfaces for compatibility with Linux, BSD, and
+glibc functionality.
+
+For basic installation instructions, see the included INSTALL file.
+Information on full musl-targeted compiler toolchains, system
+bootstrapping, and Linux distributions built on musl can be found on
+the project website:
+
+    http://www.musl-libc.org/