Updated "mirage configure --xen" for new Mini-OS and libm

We now get these via pkg-config.
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'
...
Convert from ELF to binary format (for ARM)
rework the ENTROPY signature, give evented semantics
Merge pull request #261 from mirage/evented-entropy

Move the ENTROPY sig to evented semantics
change mirage tool to apply Entropy_unix functor
disambiguate module names
Revert "disambiguate module names"

This reverts commit 76d409c5ec3bd11825a85bbbc71a02c2de3af705.
Merge pull request #262 from mirage/new-entropy-sig

Change mirage tool to apply Entropy_unix functor
Release 1.2.0
Abort the build early if pkg-config dependencies are missing
Get pkg-config dependencies from OPAM
Merge pull request #247 from talex5/arm-preview

ARM support
Fork V1 types into V2 (no other change yet)

Related to #203

Signed-off-by: David Scott <dave.scott@citrix.com>
Merge pull request #267 from djs55/fork-v2

Fork V1 types into V2 (no other change yet)
Updated to use libminios-xen >= 0.2

This adds hardware floating point and stack overflow detection on ARM.
Merge pull request #268 from talex5/libminios-xen-0.2

Update to use libminios-xen >= 0.2
Set on_crash = 'preserve' in default Xen config

Without this, if a domain crashes quickly at startup Xen may not be
able to attach to the console fast enough to display the error.
Merge pull request #270 from talex5/on_crash

Set on_crash = 'preserve' in default Xen config
Revert "Do not implicitely manage the installation of OPAM packages with the mirage tool"

We need the dependencies installed to calculate the linker options now.

This reverts commit c5355482a2f4efe473e0eb09fae73be7a8cb4432.