configure: Only text the makecontext signature we need

[fweimer-rh]

The test/explicit-bzero.c test uses a start routine without any arguments. There is no need for the multi-argument version.

This avoids a build failure with glibc and future compilers. The GNU C library declares the makecontext callback of type void (*) (void), so no cast is needed. On other systems, the type may be the (currently distinct) type void (*) (), but given that this only affects the ability to execute a test, no further machinery is added here to detect that different type.

Related to:

• https://fedoraproject.org/wiki/Changes/PortingToModernC
• https://fedoraproject.org/wiki/Toolchain/PortingToModernC

[neverpanic]

There's a typo in the commit message ("Only text …" instead of "Only test …"). Maybe whoever ends up merging this can amend the commit and fix that before merging.