Link libgcc.a

This is needed on ARM. Without it, you get:

_build/main.native.o: In function `.L104':
camlinternalOO.o:(.text+0xb36c): undefined reference to `__aeabi_dcmpge'
camlinternalOO.o:(.text+0xb3a0): undefined reference to `__aeabi_dadd'
...

Author: talex5

README.md

@@ -26,7 +26,7 @@ To work with Mirage, you'll need the following prerequisites installed:
 
 * a working [OCaml](http://ocaml.org) compiler (4.00.1 or higher).
 * the [OPAM](https://opam.ocaml.org) source package manager (1.1.1 or higher).
-* a 64-bit Linux host to compile Xen kernels, or FreeBSD, OpenBSD or MacOS X
+* an x86\_64 or armel Linux host to compile Xen kernels, or FreeBSD, OpenBSD or MacOS X
   for the userlevel version.
 
 There are three stages to using `mirage`:

lib/mirage.ml

@@ -1501,7 +1501,8 @@ let configure_makefile t =
       append oc "\tld -d -static -nostdlib --start-group \\\n\
                  \t  $(shell pkg-config --static --libs openlibm libminios) \\\n\
                  \t  _build/main.native.o %s/libocaml.a \\\n\
-                 \t  %s/libxencaml.a --end-group -o mir-%s.xen"
+                 \t  %s/libxencaml.a --end-group \\\n\
+                 \t  $(shell gcc -print-libgcc-file-name) -o mir-%s.xen"
         lib lib t.name;
     | `Unix ->
       append oc "build: main.native";