gosigar won't build for IOS

[andrewkroh]

libproc is not available in the IOS SDK. The build tags on the files could be updated to include the sigar_stub.go and exclude the darwin files to word-around the issue for any projects that use this library.

If this is pursued then the project should add a test that compiles work for

GOOS=darwin GOOS=amd64 go build .
GOOS=darwin GOOS=386 go build .
gomobile build -target=ios .

The README should also be updated to include a note about IOS.

[andrewkroh]

Relates: #134

[birros]

I found a tricky way to make ios build. I added a cgo flags with include dir pointing to macOS sdk where libproc.h is located.

I'm not doing a pull request because I don't know if you accept this trick, it's not a fix. I'll let you choose if it's relevant.

package gosigar

/*
#cgo CFLAGS: -I/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include
#include <libproc.h>
*/
import "C"

Example: birros/gosigar/blob/v0.12.0-fix-ios/sigar_darwin.go#L6