Add thin abstraction layer for processes and filesystem

This is used instead of some hardcoded Unix calls and means this code
now works on Windows

(This is a rework of a previous patch which used boost, now that I have
been informed that we are trying to move towards removing boost).

Change-Id: Ib0d11055279bbd7b710f086e9890369e3ecbfe9a
Signed-off-by: Robert Hughes <robert.hughes@arm.com>
diff --git a/Android.mk b/Android.mk
index 8f348d9..60d1f7b 100644
--- a/Android.mk
+++ b/Android.mk
@@ -118,6 +118,8 @@
         src/armnnUtils/TensorUtils.cpp \
         src/armnnUtils/VerificationHelpers.cpp \
         src/armnnUtils/NetworkSockets.cpp \
+        src/armnnUtils/Filesystem.cpp \
+        src/armnnUtils/Processes.cpp \
         src/armnn/layers/AbsLayer.cpp \
         src/armnn/layers/ActivationLayer.cpp \
         src/armnn/layers/AdditionLayer.cpp \