libc: Fix constants used by libc::pathconf

`_PC_NAME_MAX` is necessary to use `libc::pathconf`. Its value is fixed
to 3 currently, but actually it varies with the platform.

* _PC_NAME_MAX == 3

Linux (glibc): https://sourceware.org/git/?p=glibc.git;a=blob;f=bits/confname.h;h=1c714dfbf9398b8a600f9b69426a7ad8c7e89ab4;hb=HEAD#l32
NaCl (newlib): https://chromium.googlesource.com/native_client/nacl-newlib/+/373135ec5241d09138aa56603742b94b3b64ea1d/newlib/libc/include/sys/unistd.h#430

* _PC_NAME_MAX == 4

Android (Bionic): https://github.com/android/platform_bionic/blob/7e919daeaad62515ebbbf7b06badc77625a14d90/libc/include/unistd.h#L59
FreeBSD: https://svnweb.freebsd.org/base/head/sys/sys/unistd.h?revision=239347&view=markup#l127
NetBSD: http://ftp.netbsd.org/pub/NetBSD/NetBSD-current/src/sys/sys/unistd.h
OS X: http://opensource.apple.com/source/xnu/xnu-2782.10.72/bsd/sys/unistd.h

This commit fixes this, and also addes the `_PC_PATH_MAX` constant
needed by further commits.

src/liblibc/lib.rs

@@ -3920,6 +3920,8 @@ pub mod consts {
             pub const _SC_XBS5_ILP32_OFFBIG : c_int = 126;
             pub const _SC_XBS5_LPBIG_OFFBIG : c_int = 128;
 
+            pub const _PC_NAME_MAX: c_int = 3;
+            pub const _PC_PATH_MAX: c_int = 4;
         }
         #[cfg(target_os = "nacl")]
         pub mod sysconf {
@@ -3928,6 +3930,9 @@ pub mod consts {
             pub static _SC_SENDMSG_MAX_SIZE : c_int = 0;
             pub static _SC_NPROCESSORS_ONLN : c_int = 1;
             pub static _SC_PAGESIZE : c_int = 2;
+
+            pub const _PC_NAME_MAX: c_int = 3;
+            pub const _PC_PATH_MAX: c_int = 4;
         }
 
         #[cfg(target_os = "android")]
@@ -3963,6 +3968,9 @@ pub mod consts {
             pub const _SC_STREAM_MAX : c_int = 27;
             pub const _SC_TZNAME_MAX : c_int = 28;
             pub const _SC_PAGESIZE : c_int = 39;
+
+            pub const _PC_NAME_MAX: c_int = 4;
+            pub const _PC_PATH_MAX: c_int = 5;
         }
     }
 
@@ -4433,6 +4441,9 @@ pub mod consts {
             pub const _SC_SEM_VALUE_MAX : c_int = 50;
             pub const _SC_SIGQUEUE_MAX : c_int = 51;
             pub const _SC_TIMER_MAX : c_int = 52;
+
+            pub const _PC_NAME_MAX: c_int = 4;
+            pub const _PC_PATH_MAX: c_int = 5;
         }
     }
 
@@ -4868,6 +4879,9 @@ pub mod consts {
             pub const _SC_SYNCHRONIZED_IO : c_int = 75;
             pub const _SC_TIMER_MAX : c_int = 93;
             pub const _SC_TIMERS : c_int = 94;
+
+            pub const _PC_NAME_MAX: c_int = 4;
+            pub const _PC_PATH_MAX: c_int = 5;
         }
     }
 
@@ -5379,6 +5393,9 @@ pub mod consts {
             pub const _SC_TRACE_SYS_MAX : c_int = 129;
             pub const _SC_TRACE_USER_EVENT_MAX : c_int = 130;
             pub const _SC_PASS_MAX : c_int = 131;
+
+            pub const _PC_NAME_MAX: c_int = 4;
+            pub const _PC_PATH_MAX: c_int = 5;
         }
     }
 }
@@ -5835,8 +5852,6 @@ pub mod funcs {
             use types::os::arch::posix88::{gid_t, off_t, pid_t};
             use types::os::arch::posix88::{ssize_t, uid_t};
 
-            pub const _PC_NAME_MAX: c_int = 4;
-
             #[cfg(not(target_os = "nacl"))]
             extern {
                 pub fn access(path: *const c_char, amode: c_int) -> c_int;