[update] add Android support for API 16+

[mangel9742]

Concerning the issue : #127
memalign was added for Android API since version 16. Adding this permits us to build c4core in android_armv8 and android_x86_64.

[biojppm]

Thanks!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (47ba0fa) 96.99% compared to head (4a93948) 96.98%.
Report is 2 commits behind head on master.

❗ Current head 4a93948 differs from pull request most recent head 7618abf. Consider uploading reports for the commit 7618abf to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #129      +/-   ##
==========================================
- Coverage   96.99%   96.98%   -0.01%     
==========================================
  Files          28       28              
  Lines        3129     3119      -10     
==========================================
- Hits         3035     3025      -10     
  Misses         94       94              

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[biojppm]

@mangel9742 I need to update the changelog. Can you either enable the checkbox "Allow edits by maintainers" in your PR page, or (failing that) add this to changelog/current.md?

----------------------------- changelog/current.md -----------------------------
index 0d29ce4..cf759f4 100644
@@ -20,6 +20,7 @@ assert(to_substr(arr).len == 9);
 assert(to_substr((char*)ptr).len == 3); // as before
 ```
 
+
 ### New features
 
 - [#PR101](https://github.com/biojppm/c4core/pulls/101): For `substr` and `csubstr`:
@@ -51,6 +52,7 @@ assert(to_substr((char*)ptr).len == 3); // as before
 
 ### Fixes
 
+- [PR#129](https://github.com/biojppm/c4core/pull/129) - Support android by enabling `aalloc()`'s call to `memalign()`, available for API 16+.
 - [PR#115](https://github.com/biojppm/c4core/pull/115) - Refactor of `c4::blob`/`c4::cblob`. Use SFINAE to invalidate some of the constructors.
 - [PR#110](https://github.com/biojppm/c4core/pull/110)/[PR#107](https://github.com/biojppm/c4core/pull/107) - Update fast_float.
 - [PR#108](https://github.com/biojppm/c4core/pull/108) - Fix preprocessor concatenation of strings in `C4_NOT_IMPLEMENTED_MSG()` and `C4_NOT_IMPLEMENTED_IF_MSG()`.
@@ -62,3 +64,8 @@ assert(to_substr((char*)ptr).len == 3); // as before
 - Inject explicit `#include <charconv>` on the amalgamated header. The amalgamation tool was filtering all prior includes, thus causing a compilation error. Addresses [rapidyaml#364](https://github.com/biojppm/rapidyaml/issues/364).
 - [PR#117](https://github.com/biojppm/c4core/pull/117): Windows: fix compilation with MSVC/clang++.
 - Windows: add missing `C4CORE_EXPORT` to `c4::base64_valid()`, `c4::base64_encode()` and `c4::base64_decode()`.
+
+
+### Thanks
+
+- @mangel9742