Doc: add a note about Rustc's minimum MACOSX_DEPLOYMENT_TARGET requirement (#2326)

* doc: add a note about rustc's minimum MACOSX_DEPLOYMENT_TARGET requirement

* Update docs/platforms/macos.md

* Update faq.md

---------

Co-authored-by: Henry Schreiner <HenrySchreinerIII@gmail.com>

docs/faq.md

@@ -294,7 +294,16 @@ CIBW_BEFORE_ALL_WINDOWS: rustup target add i686-pc-windows-msvc
 CIBW_ENVIRONMENT_LINUX: "PATH=$HOME/.cargo/bin:$PATH"
 ```
 
-Rust does not provide Cargo for musllinux 32-bit, so that needs to be skipped:
+Rust's minimum macOS target is 10.12, while CPython supports 10.9 before
+Python 3.12, so you'll need to raise the minimum:
+
+```toml
+[tool.cibuildwheel.macos.environment]
+MACOSX_DEPLOYMENT_TARGET = "10.12"
+```
+
+And Rust does not provide Cargo for musllinux 32-bit, so that needs to be
+skipped:
 
 ```toml
 [tool.cibuildwheel]

docs/platforms/macos.md

@@ -41,6 +41,12 @@ macOS builds will honor the `MACOSX_DEPLOYMENT_TARGET` environment variable to c
 
 If you set the value lower, cibuildwheel will cap it to the lowest supported value for each target as needed.
 
+!!! note
+    For Rust-based extensions, `Rustc` requires `MACOSX_DEPLOYMENT_TARGET` to be at
+    least 10.12. However, `cibuildwheel` defaults to 10.9 for
+    **Intel / CPython 3.8-3.11** builds. Users must manually set
+    `MACOSX_DEPLOYMENT_TARGET` to 10.12 or higher when building Rust extensions.
+
 ## Universal builds
 
 By default, macOS builds will build a single architecture wheel, using the build machine's architecture. If you need to support both x86_64 and Apple Silicon, you can use the `CIBW_ARCHS` environment variable to specify the architectures you want to build, or the value `universal2` to build a multi-architecture wheel. cibuildwheel will test x86_64 wheels (or the x86_64 slice of a `universal2` wheel) when running on Apple Silicon hardware, but it is *not* possible to test Apple Silicon wheels on x86_64 hardware.