This adds stack markings to the missing fmod .S files, otherwise the
final libopenlibm object file gets marked with an executable stack.
Output when compiling from source on Gentoo Linux:
```
* QA Notice: The following files contain writable and executable sections
* Files with such sections will not work properly (or at all!) on some
* architectures/operating systems. A bug should be filed at
* https://bugs.gentoo.org/ to make sure the issue is fixed.
* For more information, see:
*
* https://wiki.gentoo.org/wiki/Hardened/GNU_stack_quickstart
*
* Please include the following list of files in your report:
* Note: Bugs should be filed for the respective maintainers
* of the package in question and not hardened@gentoo.org.
* RWX --- --- usr/lib64/libopenlibm.so.4.0
```
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