Exclude libgcc and libunwind from linked libraries on Android.

[mgautierfr]

As said in [1], unwinder is linked automatically by Clang and shared library must not re-export it.

ndk after r23 (we are using r21) should do this. Else we must take care to not re-export it.

From [2], we should pass the flags Wl,--exclude-libs,libgcc.a and -Wl,--exclude-libs,libunwind.a to avoid re-export _Unwind_Resume methods.

Fix https://github.com/kiwix/kiwix-android/issues/3661

[1] https://android.googlesource.com/platform/ndk/+/master/docs/BuildSystemMaintainers.md#Unwinding [2] https://github.com/android/ndk/issues/889#issuecomment-464334469

[kelson42]

@mgautierfr I guess it fixes the unwind error, but not the crash scenario?

[mgautierfr]

@MohitMaliFtechiz, can you test with build libraries in https://tmp.kiwix.org/ci/dev_preview/fix_android_compilation please ?

I guess it fixes the unwind error, but not the crash scenario?

The crash is due to the broken unwind. So it also fixes the crash. A small repro case made by @MohitMaliFtechiz now don't crash on my side with this fix.

[MohitMaliFtechiz]

@mgautierfr, @kelson42 I have tested the test binary that you provided me and also with the https://tmp.kiwix.org/ci/dev_preview/fix_android_compilation, and the application is not crashing with these binary on the arm architecture. I can read the zim file without crashing. Also, the testZim is now starts showing on the library screen so the crash scenario is fixed for the arm architecture.

[mgautierfr]

Perfect. I'm merging.