fix compilation with MSYS2

[neheb]

First change fixes a redefinition error.

Second one fixes missing definition for EINVAL and such.

Signed-off-by: Rosen Penev rosenp@gmail.com

remaining warnings:

../subprojects/libkqueue-2.6.1/src/common/private.h:105:9: warning: 'VISIBLE' macro redefined [-Wmacro-redefined]
#define VISIBLE         __attribute__((visibility("default")))
        ^
../subprojects/libkqueue-2.6.1/src/common/../windows/platform.h:110:9: note: previous definition is here
#define VISIBLE __declspec(dllexport)
        ^
In file included from ../subprojects/libkqueue-2.6.1/src/common/libkqueue.c:16:
../subprojects/libkqueue-2.6.1/src/common/private.h:106:9: warning: 'HIDDEN' macro redefined [-Wmacro-redefined]
#define HIDDEN          __attribute__((visibility("hidden")))
        ^
../subprojects/libkqueue-2.6.1/src/common/../windows/platform.h:111:9: note: previous definition is here
#define HIDDEN
        ^
2 warnings generated.