Get rid of cfg_aliases build dependency

As it turns out cfg_aliases does a borderline trivial thing, in that it
basically just checks an environment variable and emits one or two lines
of 'cargo:' directives. When a build system other than Cargo is used
that does not honor build scripts we end up having to craft similar
logic ourselves. In such an instance, all cfg_aliases does is obfuscate
what is really going on.
So we might as well just include the logic ourselves and get rid of the
build dependency, given that we have to do it in one shape or form
anyway.

Signed-off-by: Daniel Müller <deso@posteo.net>

Cargo.toml

@@ -116,9 +116,6 @@ codegen-units = 1
 lto = false
 codegen-units = 256
 
-[build-dependencies]
-cfg_aliases = "0.2.1"
-
 [dependencies]
 cpp_demangle = {version = "0.4", optional = true}
 gimli = {version = "0.31", optional = true}

build.rs

@@ -1,7 +1,10 @@
-use cfg_aliases::cfg_aliases;
+use std::env;
+
 
 fn main() {
-    cfg_aliases! {
-        linux: { any(target_os = "linux", target_os = "android") },
+    let target_os = env::var("CARGO_CFG_TARGET_OS").unwrap();
+    if target_os == "linux" || target_os == "android" {
+        println!("cargo:rustc-cfg=linux");
     }
+    println!("cargo:rustc-check-cfg=cfg(linux)");
 }