Quite a few functions are declared with that attribute, and VS 2019
complains if the definition does not repeat it.
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
The include-what-you-use (IWYU) policy is beneficial to faster
compilation and fewer recompilations. Many build tools, such as GNU make,
provide a mechanism for automatically figuring out what .h files a .cc
file depends on. These mechanisms typically look at #include lines. When
unnecessary #includes are listed, the build system is more likely to
recompile in cases where it is not necessary.
With the enforcement, header file <include/mimalloc.h> no longer
includes <stdlib.h>.
Reference:
https://github.com/include-what-you-use/include-what-you-use/blob/master/docs/WhyIWYU.md
