build.rs: Disable LTO if enabled implictly

LTO between Rust and C is complicated. It requires clang and specific
invocations configurations for both Rust and C compilations.
If the CFLAGS from the environment enable LTO, for example from
distribution build tools this can lead to errors.
Instead always disable LTO for the C compilation. There is not much to
optimize away anyways.

Closes briansmith#1444

Author: t-8ch

build.rs

@@ -597,6 +597,8 @@ fn configure_cc(c: &mut cc::Build, target: &Target, c_root_dir: &Path, include_d
     if target.force_warnings_into_errors {
         c.warnings_into_errors(true);
     }
+
+    c.flag_if_supported("-fno-lto");
 }
 
 fn nasm(file: &Path, arch: &str, include_dir: &Path, out_dir: &Path, c_root_dir: &Path) {