Exclude libgcc and libunwind from linked library on Android.

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 be 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 kiwix/kiwix-android#3661

[1] https://android.googlesource.com/platform/ndk/+/master/docs/BuildSystemMaintainers.md#Unwinding
[2] android/ndk#889 (comment)

kiwixbuild/configs/android.py

@@ -45,7 +45,11 @@ def install_path(self):
         return self.ndk_builder.install_path
 
     def get_cross_config(self):
-        extra_libs = ["-llog"]
+        extra_libs = [
+            "-llog",
+            "-Wl,--exclude-libs,libgcc.a",
+            "-Wl,--exclude-libs,libunwind.a",
+        ]
         extra_cflags = [
             "-I{}".format(include_dir) for include_dir in self.get_include_dirs()
         ]