compile fixes

[justinc1]

I had to apply those small changes to be able to execute opam install -j4 -y libmonda-gdb.

[justinc1]

When I try to 'opam install mirage' I get errors like:

=-=- Processing actions -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
∗  installed base-num.base
∗  installed num.0
∗  installed conf-m4.1
∗  installed ocamlfind.1.7.3-1
∗  installed base-bytes.base
∗  installed ocamlbuild.0.12.0
∗  installed uchar.0.0.2
∗  installed ocamlgraph.1.8.8
∗  installed jbuilder.1.0+beta18
[ERROR] The compilation of ppx_derivers failed at "jbuilder build -p ppx_derivers -j 4".
[ERROR] The compilation of result failed at "jbuilder build -p result -j 4".
[ERROR] The compilation of ppx_traverse_builtins failed at "jbuilder build -p ppx_traverse_builtins -j 4".
[ERROR] The compilation of ocaml-compiler-libs failed at "jbuilder build -p ocaml-compiler-libs -j 4".
[ERROR] The compilation of sexplib failed at "jbuilder build -p sexplib -j 4".

#=== ERROR while installing ocaml-compiler-libs.v0.10.0 =======================#
# opam-version 1.2.2
# os           linux
# command      jbuilder build -p ocaml-compiler-libs -j 4
# path         /home/xlab/.opam/4.05.0+monda/build/ocaml-compiler-libs.v0.10.0
# compiler     4.05.0+monda
# exit-code    1
# env-file     /home/xlab/.opam/4.05.0+monda/build/ocaml-compiler-libs.v0.10.0/ocaml-compiler-libs-1840-8de6af.env
# stdout-file  /home/xlab/.opam/4.05.0+monda/build/ocaml-compiler-libs.v0.10.0/ocaml-compiler-libs-1840-8de6af.out
# stderr-file  /home/xlab/.opam/4.05.0+monda/build/ocaml-compiler-libs.v0.10.0/ocaml-compiler-libs-1840-8de6af.err
### stderr ###
# [...]
# /tmp/camlstartup5fa0cf.s: Assembler messages:
# /tmp/camlstartup5fa0cf.s:113: Error: can't resolve `caml_startup__code_end' {*UND* section} - `caml_startup__code_begin' {*UND* section}
# File "caml_startup", line 1:
# Error: Assembler error, input left in file /tmp/camlstartup5fa0cf.s
#     ocamlopt src/shadow/ocaml_shadow.cmxs (exit 2)
# (cd _build/default && /home/xlab/.opam/4.05.0+monda/bin/ocamlopt.opt -w -40 -safe-string -w -49 -g -shared -linkall -I src/shadow -o src/shadow/ocaml_shadow.cmxs src/shadow/ocaml_shadow.cmxa)
# /tmp/camlstartupa691a3.s: Assembler messages:
# /tmp/camlstartupa691a3.s:113: Error: can't resolve `caml_startup__code_end' {*UND* section} - `caml_startup__code_begin' {*UND* section}
# File "caml_startup", line 1:
# Error: Assembler error, input left in file /tmp/camlstartupa691a3.s


#=== ERROR while installing ppx_derivers.1.0 ==================================#
# opam-version 1.2.2
...
xlab@or-mir-1:~$ ocaml -version
The OCaml toplevel, version 4.05.0+dev0-2016-08-01

I have no idea if this is related to this pull request (I have zero OCaml knowledge). I was able to install, compile and run mirage with 4.05.0 switch.