Auto merge of #35060 - japaric:arm-musl, r=alexcrichton

Add ARM MUSL targets

Rebase of #33189.

I tested this by producing a std for `arm-unknown-linux-musleabi` then I cross compiled Hello world to said target. Checked that the produced binary was statically linked and verified that the binary worked under QEMU.

This depends on rust-lang/libc#341. I'll have to update this PR after that libc PR is merged.

I'm also working on generating ARM musl cross toolchain via crosstool-ng. Once I verified those work, I'll send a PR to rust-buildbot.

r? @alexcrichton
cc @timonvo

2 files changed, 11 insertions, 2 deletions

diff --git a/src/liballoc_jemalloc/Cargo.toml b/src/liballoc_jemalloc/Cargo.toml
index 768a0c2c0a5..25b3c8a3a0a 100644
--- a/src/liballoc_jemalloc/Cargo.toml
+++ b/src/liballoc_jemalloc/Cargo.toml
@@ -16,7 +16,7 @@ libc = { path = "../rustc/libc_shim" }
 
 [build-dependencies]
 build_helper = { path = "../build_helper" }
-gcc = "0.3.17"
+gcc = "0.3.27"
 
 [features]
 debug = []
diff --git a/src/liballoc_jemalloc/build.rs b/src/liballoc_jemalloc/build.rs
index d1b3583d256..dc1b8d6ea98 100644
--- a/src/liballoc_jemalloc/build.rs
+++ b/src/liballoc_jemalloc/build.rs
@@ -73,7 +73,16 @@ fn main() {
                    .replace("\\", "/"))
        .current_dir(&build_dir)
        .env("CC", compiler.path())
-       .env("EXTRA_CFLAGS", cflags)
+       .env("EXTRA_CFLAGS", cflags.clone())
+       // jemalloc generates Makefile deps using GCC's "-MM" flag. This means
+       // that GCC will run the preprocessor, and only the preprocessor, over
+       // jemalloc's source files. If we don't specify CPPFLAGS, then at least
+       // on ARM that step fails with a "Missing implementation for 32-bit
+       // atomic operations" error. This is because no "-march" flag will be
+       // passed to GCC, and then GCC won't define the
+       // "__GCC_HAVE_SYNC_COMPARE_AND_SWAP_4" macro that jemalloc needs to
+       // select an atomic operation implementation.
+       .env("CPPFLAGS", cflags.clone())
        .env("AR", &ar)
        .env("RANLIB", format!("{} s", ar.display()));