[QNN EP] Fix cmake build crashes in static_lib mode and ort_core prebuilt path

[qti-mbadnara]

Description

Fixes two cmake defects that crash the build when using --use_qnn static_lib via the ort_core prebuilt path: an unguarded cmake -E copy on an empty QNN_LIB_FILES list, and a missing --skip_submodule_sync flag that causes build.py to run git submodule sync on a non-git source tree.

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Motivation & Context

Both issues manifest only in the onnxruntime_prebuilt.cmake ExternalProject build path and were worked around locally by commenting out code and manually patching the build command — fragile fixes invisible to CI.

Issue 1 — empty QNN_LIB_FILES copy

QNN_LIB_FILES is populated by a file(GLOB ...) inside an if(MSVC OR Linux) block in microsoft/onnxruntime cmake/CMakeLists.txt. On Android / static_lib builds that block is skipped, leaving the variable undefined (empty list).

In cmake/onnxruntime_unittests.cmake (upstream), the block that copies QNN libraries to the Java native-test directory is guarded only by if(onnxruntime_USE_QNN). With QNN_LIB_FILES empty, CMake generates:

cmake -E copy <destination>

cmake -E copy requires at least one source argument before the destination. With zero sources it prints its usage banner and exits non-zero, crashing the build.

Issue 2 — missing --skip_submodule_sync

ort_core is fetched as a URL zip archive (microsoft/onnxruntime v1.27.0) — the extracted tree has no .git directory.
build.py unconditionally runs git submodule sync --recursive regardless, crashing with:

fatal: not a git repository (or any of the parent directories): .git

build.py exposes --skip_submodule_sync exactly for this scenario, but it was never appended to ORT_BUILD_COMMAND in this repo.

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[minfhong-qti]

I thought QNN EP is always built as shared lib. Why --use_qnn static_lib is ever used?

[qti-mbadnara]

I thought QNN EP is always built as shared lib. Why --use_qnn static_lib is ever used?

It is used for Android builds.