Tweak opus build flags and allocs

This gets us to ~40% of one core cpu usage during playback. Good enough
for a while I reckon!

Paid for the internal ram usage by reclaiming some stack size headroom.

lib/opusfile/CMakeLists.txt

@@ -11,6 +11,11 @@ set(CMAKE_POLICY_DEFAULT_CMP0077 NEW)
 
 set(OPUS_FIXED_POINT ON)
 set(OPUS_ENABLE_FLOAT_API OFF)
+
+set(OPUS_VAR_ARRAYS OFF)
+set(OPUS_USE_ALLOCA ON)
+set(OPUS_NONTHREADSAFE_PSEUDOSTACK OFF)
+
 set(OPUS_INSTALL_PKG_CONFIG_MODULE OFF)
 set(OPUS_INSTALL_CMAKE_CONFIG_MODULE OFF)
 set(OPUS_BUILD_TESTING OFF)
@@ -18,5 +23,6 @@ set(OPUS_BUILD_SHARED_LIBS OFF)
 
 add_subdirectory($ENV{PROJ_PATH}/lib/opus ${CMAKE_CURRENT_BINARY_DIR}/opus)
 target_compile_definitions(opus PRIVATE CUSTOM_SUPPORT)
+target_compile_options(opus PRIVATE -Os -DSMALL_FOOTPRINT -funroll-loops -ffast-math)
 target_include_directories(opus PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/include)
 target_link_libraries(${COMPONENT_LIB} PUBLIC opus)