refactor: pull repr out of BuildOptions

cibuildwheel/__main__.py

@@ -406,8 +406,7 @@ def print_preamble(platform: str, build_options: BuildOptions) -> None:
 
     print("Build options:")
     print(f"  platform: {platform!r}")
-    for option, value in sorted(build_options._asdict().items()):
+    print(textwrap.indent(str(build_options), "  "))
-        print(f"  {option}: {value!r}")
 
     warnings = detect_warnings(platform, build_options)
     if warnings:

cibuildwheel/util.py

@@ -225,6 +225,10 @@ class BuildOptions(NamedTuple):
     build_verbosity: int
     build_frontend: BuildFrontend
 
+    def __str__(self) -> str:
+        res = (f"{option}: {value!r}" for option, value in sorted(self._asdict().items()))
+        return "\n".join(res)
+
 
 class NonPlatformWheelError(Exception):
     def __init__(self) -> None: