PTHREAD_SCOPE_SYSTEM configure check fails with Clang 16 (-Wimplicit-int)

[thesamesam]

Bug report

The PTHREAD_SCOPE_SYSTEM configure check lacks int before the main() definition and causes Clang to emit a -Wimplicit-int warning. This warning becomes an error by default with Clang 16+.

Your environment

• CPython versions tested on: master
• Operating system and architecture: Gentoo Linux amd64
• Clang 16 (or Clang 15 with -Werror=implicit-int -Werror=implicit-function-declaration)

• PR: gh-99086: Fix implicit int warning in configure check for PTHREAD_SCOPE_SYSTEM (#99085) #99085

• PR: [3.11] gh-99086: Fix implicit int compiler warning in configure check for PTHREAD_SCOPE_SYSTEM (GH-99085) #99118

• PR: [3.10] gh-99086: Fix implicit int compiler warning in configure check for PTHREAD_SCOPE_SYSTEM (GH-99085) #99119

• PR: gh-99086: Fix -Wstrict-prototypes, -Wimplicit-function-declaration warnings in configure.ac #99406

• PR: [3.11] gh-99086: Fix -Wstrict-prototypes, -Wimplicit-function-declara… #99919

• PR: [3.10] GH-99086: Fix -Wstrict-prototypes, -Wimplicit-function-declara… #99920