perf: pass --no-compile for build deps (#13192)

As the build environment is ephemeral, it's wasteful to pre-compile
everything, especially as not every Python module will be used/compiled
in most cases. In addition, the argument is that compilation ensures
read-only installations are not slower than necessary is moot as the
build environment is by design writable.

This saves ~200ms while installing setuptools while building pip itself.
For context, a pip install . (with --no-index and --find-links) takes
3400ms on main and pip wheel . takes 2200ms on main.

So, it's not a major win, but it's also nothing to sneeze at. Packages
using smaller backends, like flit, will likely see smaller improvements.

Author: ichard26

news/7294.feature.rst

@@ -0,0 +1,2 @@
+Build environment dependencies are no longer compiled to bytecode during
+installation for a minor performance improvement.

src/pip/_internal/build_env.py

@@ -240,6 +240,10 @@ def _install_requirements(
             prefix.path,
             "--no-warn-script-location",
             "--disable-pip-version-check",
+            # As the build environment is ephemeral, it's wasteful to
+            # pre-compile everything, especially as not every Python
+            # module will be used/compiled in most cases.
+            "--no-compile",
             # The prefix specified two lines above, thus
             # target from config file or env var should be ignored
             "--target",