build: add Android x86_64 support to Makefile

[glitchminer]

Android x86_64 support is required for testing on LambdaTest with virtual devices. This PR:

• Sets MOBILE_GOARCH to amd64 when ARCH is x86_64
• Sets ANDROID_CLANG_TARGET to x86_64-linux-android

Closes #6989

[status-im-auto]

Jenkins Builds

❔	Commit	#️⃣	Finished (UTC)	Duration	Platform	Result
✔️	bfc1687	#1	2025-10-08 14:46:36	~3 min	macos/status-go	📦zip
✔️	bfc1687	#1	2025-10-08 14:46:50	~3 min	linux/status-go	📦zip
✔️	bfc1687	#1	2025-10-08 14:49:02	~5 min	windows/status-go	📦zip
✔️	bfc1687	#1	2025-10-08 14:54:07	~11 min	linux/nwaku	📦zip
✔️	bfc1687	#1	2025-10-08 14:54:16	~11 min	tests-rpc	📄log
✔️	bfc1687	#1	2025-10-08 15:10:18	~27 min	tests	📄log

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 59.37%. Comparing base (c3bd89f) to head (bfc1687).
⚠️ Report is 1 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #6990      +/-   ##
===========================================
+ Coverage    55.13%   59.37%   +4.24%     
===========================================
  Files          820      821       +1     
  Lines       116624   116626       +2     
===========================================
+ Hits         64301    69252    +4951     
+ Misses       45535    40253    -5282     
- Partials      6788     7121     +333     

Flag	Coverage Δ
functional	33.80% <ø> (?)
unit	55.11% <ø> (-0.02%)	⬇️

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see 211 files with indirect coverage changes