build, qt: Native Qt builds in depends do not work #21588

macOS

When doing % make -C depends qt_configured the native build is expected:

Configure summary:

Build type: macx-clang (x86_64, CPU features: cx16 mmx sse sse2 sse3 ssse3 sse4.1)
Compiler: clang (Apple) 12.0.0
Configuration: sse2 aesni sse3 ssse3 sse4_1 sse4_2 avx avx2 avx512f avx512bw avx512cd avx512dq avx512er avx512ifma avx512pf avx512vbmi avx512vl f16c largefile precompile_header rdrnd shani silent x86SimdAlways release c++11 c++14 c++1z reduce_exports static stl
Build options:
  Mode ................................... release
...

Actually, a cross-compile build is configured:

Configure summary:

Building on: macx-clang (x86_64, CPU features: cx16 mmx sse sse2 sse3 ssse3 sse4.1)
Building for: macx-clang (x86_64, CPU features: cx16 mmx sse sse2 sse3 ssse3 sse4.1)
Target compiler: clang (Apple) 12.0.0
Configuration: cross_compile sse2 aesni sse3 ssse3 sse4_1 sse4_2 avx avx2 avx512f avx512bw avx512cd avx512dq avx512er avx512ifma avx512pf avx512vbmi avx512vl f16c largefile precompile_header rdrnd shani silent x86SimdAlways release c++11 c++14 c++1z reduce_exports static stl
Build options:
  Mode ................................... release
...

The reason for this behavior is the line which was added in #21376: https://github.com/bitcoin/bitcoin/blob/e08f3193b543017702d000c2263bccbefa981c14/depends/packages/qt.mk#L116 as the -device-option is a cross-compile option, and it triggers cross-compiling.

It is worth to mention that before #21376 native builds with depends on macOS were broken (#14648, #19785).

Linux x86

Again, no native build when it is expected:

$ make -C depends qt_configured
...
Configure summary:

Building on: linux-g++ (x86_64, CPU features: mmx sse sse2)
Building for: linux-g++-64 (x86_64, CPU features: mmx sse sse2)
Target compiler: gcc 9.3.0
Configuration: cross_compile sse2 aesni sse3 ssse3 sse4_1 sse4_2 avx avx2 avx512f avx512bw avx512cd avx512dq avx512er avx512ifma avx512pf avx512vbmi avx512vl enable_new_dtags f16c largefile precompile_header rdrnd shani silent x86SimdAlways release c++11 c++14 c++1z dbus reduce_exports static stl
Build options:
  Mode ................................... release
...

The reason for this behavior is the line which was added in #12971: https://github.com/bitcoin/bitcoin/blob/e08f3193b543017702d000c2263bccbefa981c14/depends/packages/qt.mk#L141 with a comment:

This should fix the gitian build issue

ARM

Just broken.

Confirming that cross-compile is attempted when trying to build natively using depends on macOS 11.2.3 and 10.15.7. I think this is why dark mode does not work when built from depends on 10.15.7.

Confirming cross-compile is attempted on linux as well (Ubuntu):

Configure summary:

Building on: linux-g++ (x86_64, CPU features: mmx sse sse2)
Building for: linux-g++-64 (x86_64, CPU features: mmx sse sse2)
Target compiler: gcc 9.3.0