feat: Update esp-idf flag

(backport <rust-lang#3993>)
(cherry picked from commit 7bd7276)

Author: SergioGasquez

build.rs

@@ -7,7 +7,7 @@ use std::str;
 // make sure to add it to this list as well.
 const ALLOWED_CFGS: &'static [&'static str] = &[
     "emscripten_new_stat_abi",
-    "espidf_time64",
+    "espidf_time32",
     "freebsd10",
     "freebsd11",
     "freebsd12",

src/unix/newlib/mod.rs

@@ -52,7 +52,7 @@ cfg_if! {
 pub type useconds_t = u32;
 
 cfg_if! {
-    if #[cfg(any(target_os = "horizon", all(target_os = "espidf", espidf_time64)))] {
+    if #[cfg(any(target_os = "horizon", all(target_os = "espidf", not(espidf_time32))))] {
         pub type time_t = ::c_longlong;
     } else {
         pub type time_t = i32;