Use __ARM_ACLE to guard inclusion of arm_acle.h

[lgoettgens]

When trying to build FLINT v3.2.0 with julia's BinaryBuilder (to produce the julia package FLINT_jll.jl that is a dependency of Nemo.jl), the build for aarch64-linux-gnu failed with the following error message:

[23:35:30] /workspace/srcdir/flint-3.2.0/src/ulong_extras/revbin.c: In function ‘n_revbin’:
[23:35:30] /workspace/srcdir/flint-3.2.0/src/ulong_extras/revbin.c:29:9: error: implicit declaration of function ‘__rbitll’ [-Werror=implicit-function-declaration]
[23:35:30]      n = __rbitll(n);
[23:35:30]          ^~~~~~~~

(full log at https://buildkite.com/julialang/yggdrasil/builds/18605#01958cb4-1ad1-4dac-87ea-34869cf00fad/689-11246)

This could be due to BinaryBuilder.jl using very old compilers for maximum compatibility of produced libraries; the above error was produced with GCC v6.

#2245 added a check wether the arm_acle.h header contains the rbit instruction. However, it does not check if the arm_acle.h header even exists in the first place.
According to https://github.com/ARM-software/acle/releases/download/r2024Q4/acle-2024Q4.pdf, Section 3.5.1, one can test this by checking for __ARM_ACLE (as this PR does).

Adding the patch from this PR to the BinaryBuilder.jl script fixed the above build failure, so I thought it would be good to upstream this.

[albinahlback]

Good catch, thanks!

[lgoettgens]

If you do another 3.2 patch release, I think this would be great to have in there. But please don't spend the time just for this patch, only if you have other reasons to do it.

[albinahlback]

I will make sure to include it if we push 3.2.2.