Improve the error for failed PEP 517 builds

The original message would result in errors like:

    Could not build wheels for xmlsec, which is required to
    install pyproject.toml-based projects

Which could be misinterpreted to mean that xmlsec is required to install
pyproject.toml-based projects, rather than that building wheels is.

This commit aims to make the error message clearer while still working
for a comma-separated list of package names.

Signed-off-by: Matt Wozniski <[email protected]>

Author: godlygeek

news/7f9639a2-df21-4e0c-9023-80f00fd71d20.trivial.rst

@@ -427,8 +427,8 @@ def run(self, options: Values, args: List[str]) -> int:
 
             if build_failures:
                 raise InstallationError(
-                    "Could not build wheels for {}, which is required to "
-                    "install pyproject.toml-based projects".format(
+                    "ERROR: Failed to build installable wheels for some "
+                    "pyproject.toml based projects ({})".format(
                         ", ".join(r.name for r in build_failures)  # type: ignore
                     )
                 )