Removing functions non-existant in uclibc (#281)

Author: plauche

crates/backtrace-sys/build.rs

@@ -12,7 +12,8 @@ fn main() {
         target.contains("cloudabi") ||
         target.contains("hermit") ||
         target.contains("wasm32") ||
-        target.contains("fuchsia")
+        target.contains("fuchsia") ||
+        target.contains("uclibc")   // not supported for uclibc
     // fuchsia uses external out-of-process symbolization
     {
         println!("cargo:rustc-cfg=empty");

src/symbolize/mod.rs

@@ -489,14 +489,16 @@ cfg_if::cfg_if! {
     } else if #[cfg(all(feature = "libbacktrace",
                         any(unix, all(windows, not(target_vendor = "uwp"), target_env = "gnu")),
                         not(target_os = "fuchsia"),
-                        not(target_os = "emscripten")))] {
+                        not(target_os = "emscripten"),
+                        not(target_env = "uclibc")))] {
         mod libbacktrace;
         use self::libbacktrace::resolve as resolve_imp;
         use self::libbacktrace::Symbol as SymbolImp;
         unsafe fn clear_symbol_cache_imp() {}
     } else if #[cfg(all(unix,
                         not(target_os = "emscripten"),
                         not(target_os = "fuchsia"),
+                        not(target_env = "uclibc"),
                         feature = "dladdr"))] {
         mod dladdr_resolve;
         use self::dladdr_resolve::resolve as resolve_imp;