build yaegi in android termux

[mvertes]

Building yaegi natively in a android host in termux (GOOS=android) leads to the following errors:

$ go build ./cmd/yaegi
# github.com/containous/yaegi/stdlib/syscall
stdlib/syscall/go1_15_syscall_linux_arm.go:2258:6: _syscall_Conn redeclared in this block
        previous declaration at stdlib/syscall/go1_15_syscall_android_arm.go:2258:6
stdlib/syscall/go1_15_syscall_linux_arm.go:2262:24: _syscall_Conn.SyscallConn redeclared in this block
        previous declaration at stdlib/syscall/go1_15_syscall_android_arm.go:2262:6
stdlib/syscall/go1_15_syscall_linux_arm.go:2265:6: _syscall_RawConn redeclared in this block
        previous declaration at stdlib/syscall/go1_15_syscall_android_arm.go:2265:6
stdlib/syscall/go1_15_syscall_linux_arm.go:2271:27: _syscall_RawConn.Control redeclared in this block
        previous declaration at stdlib/syscall/go1_15_syscall_android_arm.go:2271:6
stdlib/syscall/go1_15_syscall_linux_arm.go:2272:27: _syscall_RawConn.Read redeclared in this block
        previous declaration at stdlib/syscall/go1_15_syscall_android_arm.go:2272:6
stdlib/syscall/go1_15_syscall_linux_arm.go:2273:27: _syscall_RawConn.Write redeclared in this block
        previous declaration at stdlib/syscall/go1_15_syscall_android_arm.go:2273:6
stdlib/syscall/go1_15_syscall_linux_arm.go:2276:6: _syscall_Sockaddr redeclared in this block
        previous declaration at stdlib/syscall/go1_15_syscall_android_arm.go:2276:6

When cross-compiling, only specified OS corresponding file is taken, and there is no problem. The problems happens when compiling natively.

The problem occurs because both go1_15_syscall_linux_arm.go and go1_15_syscall_linux_arm.go are compiled. According to https://golang.org/cmd/go/#hdr-Build_constraints, this happens for android/linux and illumos/solaris.