Require rust >= 1.30 and drop libc_core_cvoid conditional

Move the `c_void` re-export to the top-level `lib.rs`.

(apply <#4060> to `main`)
(cherry picked from commit e221887)

Author: joshtriplett

src/fuchsia/mod.rs

@@ -3,6 +3,8 @@
 //! More functions and definitions can be found in the more specific modules
 //! according to the platform in question.
 
+use c_void;
+
 // PUB_TYPE
 
 pub type c_schar = i8;
@@ -4486,5 +4488,3 @@ cfg_if! {
         // Unknown target_arch
     }
 }
-
-pub use ffi::c_void;

src/hermit.rs

@@ -1,5 +1,7 @@
 //! Hermit C type definitions
 
+use c_void;
+
 cfg_if! {
     if #[cfg(any(target_arch = "aarch64", target_arch = "riscv64"))] {
         pub type c_char = u8;
@@ -576,5 +578,3 @@ extern "C" {
     #[link_name = "sys_poll"]
     pub fn poll(fds: *mut pollfd, nfds: nfds_t, timeout: i32) -> i32;
 }
-
-pub use ffi::c_void;

src/lib.rs

@@ -61,6 +61,8 @@ use core::num;
 #[allow(unused_imports)]
 use core::option::Option;
 
+pub use core::ffi::c_void;
+
 cfg_if! {
     if #[cfg(windows)] {
         mod fixed_width_ints;

src/sgx.rs

@@ -25,5 +25,3 @@ pub type c_ulong = u64;
 
 pub const INT_MIN: c_int = -2147483648;
 pub const INT_MAX: c_int = 2147483647;
-
-pub use ffi::c_void;

src/solid/mod.rs

@@ -2,6 +2,8 @@
 //!
 //! [SOLID]: https://solid.kmckk.com/
 
+use c_void;
+
 pub type c_schar = i8;
 pub type c_uchar = u8;
 pub type c_short = i16;
@@ -871,8 +873,6 @@ extern "C" {
     pub fn lseek(arg1: c_int, arg2: __off_t, arg3: c_int) -> __off_t;
 }
 
-pub use ffi::c_void;
-
 cfg_if! {
     if #[cfg(target_arch = "aarch64")] {
         mod aarch64;

src/switch.rs

@@ -27,5 +27,3 @@ pub type wchar_t = u32;
 
 pub const INT_MIN: c_int = -2147483648;
 pub const INT_MAX: c_int = 2147483647;
-
-pub use ffi::c_void;

src/unix/mod.rs

@@ -3,6 +3,8 @@
 //! More functions and definitions can be found in the more specific modules
 //! according to the platform in question.
 
+use c_void;
+
 pub type c_schar = i8;
 pub type c_uchar = u8;
 pub type c_short = i16;
@@ -1688,5 +1690,3 @@ cfg_if! {
         // Unknown target_os
     }
 }
-
-pub use ffi::c_void;

src/vxworks/mod.rs

@@ -1,5 +1,6 @@
 //! Interface to VxWorks C library
 
+use c_void;
 use core::mem::size_of;
 use core::ptr::null_mut;
 
@@ -2013,8 +2014,6 @@ pub unsafe fn posix_memalign(
     }
 }
 
-pub use ffi::c_void;
-
 cfg_if! {
     if #[cfg(target_arch = "aarch64")] {
         mod aarch64;

src/wasi/mod.rs

@@ -2,10 +2,9 @@
 // `wasi-libc` project provides multiple libraries including emulated features, but we list only basic features with `libc.a` here.
 
 use super::{Send, Sync};
+use c_void;
 use core::iter::Iterator;
 
-pub use ffi::c_void;
-
 pub type c_char = i8;
 pub type c_uchar = u8;
 pub type c_schar = i8;

src/windows/mod.rs

@@ -1,5 +1,7 @@
 //! Windows CRT definitions
 
+use c_void;
+
 pub type c_schar = i8;
 pub type c_uchar = u8;
 pub type c_short = i16;
@@ -565,8 +567,6 @@ extern "system" {
     pub fn socket(af: ::c_int, socket_type: ::c_int, protocol: ::c_int) -> SOCKET;
 }
 
-pub use ffi::c_void;
-
 cfg_if! {
     if #[cfg(all(target_env = "gnu"))] {
         mod gnu;