cmake: Add cross-compiling support

To configure CMake for cross-compiling, use
`--toolchain depends/${HOST}/toolchain.cmake` command-line option.

CMakeLists.txt

@@ -479,6 +479,19 @@ else()
   )
 endif()
 
+target_compile_definitions(core_interface INTERFACE ${DEPENDS_COMPILE_DEFINITIONS})
+target_compile_definitions(core_interface_relwithdebinfo INTERFACE ${DEPENDS_COMPILE_DEFINITIONS_RELWITHDEBINFO})
+target_compile_definitions(core_interface_debug INTERFACE ${DEPENDS_COMPILE_DEFINITIONS_DEBUG})
+
+# If the {CXX,LD}FLAGS environment variables are defined during building depends
+# and configuring this build system, their content might be duplicated.
+if(DEFINED ENV{CXXFLAGS})
+  deduplicate_flags(CMAKE_CXX_FLAGS)
+endif()
+if(DEFINED ENV{LDFLAGS})
+  deduplicate_flags(CMAKE_EXE_LINKER_FLAGS)
+endif()
+
 if(BUILD_TESTS)
   enable_testing()
 endif()
@@ -538,6 +551,12 @@ message("  test_bitcoin-qt ..................... ${BUILD_GUI_TESTS}")
 message("  bench_bitcoin ....................... ${BUILD_BENCH}")
 message("  fuzz binary ......................... ${BUILD_FUZZ_BINARY}")
 message("")
+if(CMAKE_CROSSCOMPILING)
+  set(cross_status "TRUE, for ${CMAKE_SYSTEM_NAME}, ${CMAKE_SYSTEM_PROCESSOR}")
+else()
+  set(cross_status "FALSE")
+endif()
+message("Cross compiling ....................... ${cross_status}")
 message("C++ compiler .......................... ${CMAKE_CXX_COMPILER_ID} ${CMAKE_CXX_COMPILER_VERSION}, ${CMAKE_CXX_COMPILER}")
 include(FlagsSummary)
 flags_summary()

depends/packages/qt.mk

@@ -265,13 +265,14 @@ define $(package)_build_cmds
   $(MAKE)
 endef
 
+# TODO: Investigate whether specific targets can be used here to minimize the amount of files/components installed.
 define $(package)_stage_cmds
-  $(MAKE) -C qtbase/src INSTALL_ROOT=$($(package)_staging_dir) $(addsuffix -install_subtargets,$(addprefix sub-,$($(package)_qt_libs))) && \
-  $(MAKE) -C qttools/src/linguist INSTALL_ROOT=$($(package)_staging_dir) $(addsuffix -install_subtargets,$(addprefix sub-,$($(package)_linguist_tools))) && \
+  $(MAKE) -C qtbase INSTALL_ROOT=$($(package)_staging_dir) install && \
+  $(MAKE) -C qttools INSTALL_ROOT=$($(package)_staging_dir) install && \
   $(MAKE) -C qttranslations INSTALL_ROOT=$($(package)_staging_dir) install_subtargets
 endef
 
 define $(package)_postprocess_cmds
-  rm -rf native/mkspecs/ native/lib/ lib/cmake/ && \
-  rm -f lib/lib*.la lib/*.prl plugins/*/*.prl
+  rm -rf doc/ native/lib/ && \
+  rm -f lib/lib*.la
 endef

src/CMakeLists.txt

@@ -62,6 +62,11 @@ foreach(config IN LISTS CMAKE_BUILD_TYPE CMAKE_CONFIGURATION_TYPES)
   string(TOUPPER "${config}" config)
   set(CMAKE_C_FLAGS_${config} "${CMAKE_C_FLAGS_RELWITHDEBINFO}")
 endforeach()
+# If the CFLAGS environment variable is defined during building depends
+# and configuring this build system, its content might be duplicated.
+if(DEFINED ENV{CFLAGS})
+  deduplicate_flags(CMAKE_C_FLAGS)
+endif()
 set(CMAKE_EXPORT_COMPILE_COMMANDS OFF)
 add_subdirectory(secp256k1)
 set(CMAKE_EXPORT_COMPILE_COMMANDS ON)