Use libuv errors instead of errno in unit tests

Replaced old unit tests for errno with libuv error codes UV_ENOENT
and UV_EEXIST (for os_open and os_getperms).

Added libuv include path to test/includes compiler calls - needed
to get hold of libuv headers.

test/includes/CMakeLists.txt

@@ -8,6 +8,7 @@ foreach(hfile ${PRE_HEADERS})
     OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/${post_hfile}
     COMMAND ${CMAKE_C_COMPILER} -std=c99 -E -P
       ${CMAKE_CURRENT_SOURCE_DIR}/${hfile}
+      -I${LIBUV_INCLUDE_DIRS}
       -o ${CMAKE_CURRENT_BINARY_DIR}/${post_hfile})
   list(APPEND POST_HEADERS ${post_hfile})
 endforeach()

test/includes/pre/sys/errno.h

@@ -1,4 +0,0 @@
-#include <sys/errno.h>
-
-static const int kENOENT = ENOENT;
-static const int kEEXIST = EEXIST;

test/includes/pre/uv-errno.h

@@ -0,0 +1,4 @@
+#include <uv-errno.h>
+
+static const int kUV_ENOENT = UV_ENOENT;
+static const int kUV_EEXIST = UV_EEXIST;