Adding getprogname and setprogname for all BSDs and Solaris.

Adding program_invocation_short_name for Linux (Musl and glibc).

Adding __progname for Android. This is a little different, but
is a safer alternative to using argv[0], which may not exist, and
includes Android's default application name (currently '<unknown>').

Adding these functions and externs means it is possible for all
but Windows applications to safely discover their
name, rather than rely on argv[0] parsing, /proc/self/exe, etc.

Author: raphaelcohn

src/unix/bsd/mod.rs

@@ -358,6 +358,8 @@ extern {
                       buf: *mut ::c_char,
                       buflen: ::size_t,
                       result: *mut *mut passwd) -> ::c_int;
+    pub fn getprogname() -> *const ::c_char;
+    pub fn setprogname(name: *const ::c_char);
 }
 
 cfg_if! {

src/unix/notbsd/android/mod.rs

@@ -625,6 +625,10 @@ f! {
     }
 }
 
+extern {
+    static mut __progname: *mut ::c_char;
+}
+
 extern {
     pub fn madvise(addr: *const ::c_void, len: ::size_t, advice: ::c_int)
                    -> ::c_int;

src/unix/notbsd/linux/mod.rs

@@ -474,6 +474,10 @@ f! {
     }
 }
 
+extern {
+    static mut program_invocation_short_name: *mut ::c_char;
+}
+
 #[link(name = "util")]
 extern {
     pub fn shm_open(name: *const c_char, oflag: ::c_int,

src/unix/solaris/mod.rs

@@ -901,5 +901,7 @@ extern {
                      locale: *const ::c_char,
                      base: ::locale_t) -> ::locale_t;
     pub fn uselocale(loc: ::locale_t) -> ::locale_t;
+    pub fn getprogname() -> *const ::c_char;
+    pub fn setprogname(name: *const ::c_char);
 }