move tests covering the env:: module into their own directory

ci.sh

@@ -80,7 +80,7 @@ case $HOST_TARGET in
     MIRI_TEST_TARGET=i686-unknown-linux-gnu run_tests
     MIRI_TEST_TARGET=aarch64-apple-darwin run_tests
     MIRI_TEST_TARGET=i686-pc-windows-msvc run_tests
-    MIRI_TEST_TARGET=x86_64-unknown-freebsd run_tests_minimal hello integer vec current_dir data_race env
+    MIRI_TEST_TARGET=x86_64-unknown-freebsd run_tests_minimal hello integer vec data_race env/var
     MIRI_TEST_TARGET=thumbv7em-none-eabihf MIRI_NO_STD=1 run_tests_minimal no_std # no_std embedded architecture
     ;;
   x86_64-apple-darwin)

tests/pass/env/current_exe.rs

@@ -1,4 +1,5 @@
 //@ignore-target-windows
+//@only-on-host: the Linux std implementation opens /proc/self/exe, which doesn't work cross-target
 //@compile-flags: -Zmiri-disable-isolation
 use std::env;
 

tests/pass/libc.rs

@@ -88,7 +88,7 @@ fn test_posix_realpath_errors() {
     assert_eq!(e.kind(), ErrorKind::NotFound);
 }
 
-#[cfg(any(target_os = "linux", target_os = "freebsd"))]
+#[cfg(any(target_os = "linux"))]
 fn test_posix_fadvise() {
     use std::convert::TryInto;
     use std::io::Write;
@@ -452,7 +452,7 @@ fn test_posix_mkstemp() {
 }
 
 fn main() {
-    #[cfg(any(target_os = "linux", target_os = "freebsd"))]
+    #[cfg(any(target_os = "linux"))]
     test_posix_fadvise();
 
     test_posix_gettimeofday();