Workaround presence of LLVM library in stage0/lib

This commit works around the newly-introduced LLVM shared library.

This is needed such that llvm-config run from
librustc_llvm's build script can correctly locate it's own LLVM, not the
one in stage0/lib. The LLVM build system uses the DT_RUNPATH/RUNPATH
header within the llvm-config binary, which we want to use, but because
Cargo always adds the host compiler's "libdir" (stage0/lib in our
case) to the dynamic linker's search path, we weren't properly finding
the freshly-built LLVM in llvm/lib. By restoring the environment
variable setting the search path to what bootstrap sees, the problem is
resolved and librustc_llvm correctly links and finds the appropriate
LLVM.

Several run-make-fulldeps tests are also updated with similar handling.

3 files changed, 14 insertions, 2 deletions

diff --git a/src/bootstrap/builder.rs b/src/bootstrap/builder.rs
index a69ba207495..f742bce180c 100644
--- a/src/bootstrap/builder.rs
+++ b/src/bootstrap/builder.rs
@@ -21,7 +21,7 @@ use crate::install;
 use crate::native;
 use crate::test;
 use crate::tool;
-use crate::util::{add_lib_path, exe, libdir};
+use crate::util::{self, add_lib_path, exe, libdir};
 use crate::{Build, DocTests, Mode, GitRepo};
 
 pub use crate::Compiler;
@@ -791,6 +791,13 @@ impl<'a> Builder<'a> {
             .env("CARGO_TARGET_DIR", out_dir)
             .arg(cmd);
 
+        // See comment in librustc_llvm/build.rs for why this is necessary, largely llvm-config
+        // needs to not accidentally link to libLLVM in stage0/lib.
+        cargo.env("REAL_LIBRARY_PATH_VAR", &util::dylib_path_var());
+        if let Some(e) = env::var_os(util::dylib_path_var()) {
+            cargo.env("REAL_LIBRARY_PATH", e);
+        }
+
         if cmd != "install" {
             cargo.arg("--target")
                  .arg(target);
diff --git a/src/bootstrap/compile.rs b/src/bootstrap/compile.rs
index b581271663e..ec04dee6c32 100644
--- a/src/bootstrap/compile.rs
+++ b/src/bootstrap/compile.rs
@@ -712,6 +712,7 @@ pub fn build_codegen_backend(builder: &Builder,
             if builder.is_rust_llvm(target) && backend != "emscripten" {
                 cargo.env("LLVM_RUSTLLVM", "1");
             }
+
             cargo.env("LLVM_CONFIG", &llvm_config);
             if backend != "emscripten" {
                 let target_config = builder.config.target_config.get(&target);
diff --git a/src/bootstrap/util.rs b/src/bootstrap/util.rs
index 2880f1a084b..37c6c040da8 100644
--- a/src/bootstrap/util.rs
+++ b/src/bootstrap/util.rs
@@ -70,7 +70,11 @@ pub fn dylib_path_var() -> &'static str {
 /// Parses the `dylib_path_var()` environment variable, returning a list of
 /// paths that are members of this lookup path.
 pub fn dylib_path() -> Vec<PathBuf> {
-    env::split_paths(&env::var_os(dylib_path_var()).unwrap_or_default()).collect()
+    let var = match env::var_os(dylib_path_var()) {
+        Some(v) => v,
+        None => return vec![],
+    };
+    env::split_paths(&var).collect()
 }
 
 /// `push` all components to `buf`. On windows, append `.exe` to the last component.