build: use ARCH 'native' by default, allow to configure and override it

.travis.yml

@@ -58,7 +58,7 @@ script:
     - export TRAVIS_COMMIT_LOG=`git log --format=fuller -1`
     - OUTDIR=$BASE_OUTDIR/$TRAVIS_PULL_REQUEST/$TRAVIS_JOB_NUMBER-$HOST
     - if [ -z "$NO_DEPENDS" ]; then $DOCKER_EXEC ccache --max-size=$CCACHE_SIZE; fi
-    - $DOCKER_EXEC bash -c "mkdir build && cd build && cmake -DCMAKE_TOOLCHAIN_FILE=$TRAVIS_BUILD_DIR/contrib/depends/$HOST/share/toolchain.cmake .. && make $MAKEJOBS"
+    - $DOCKER_EXEC bash -c "mkdir build && cd build && cmake -DCMAKE_TOOLCHAIN_FILE=$TRAVIS_BUILD_DIR/contrib/depends/$HOST/share/toolchain.cmake -DTRAVIS=true .. && make $MAKEJOBS"
     - export LD_LIBRARY_PATH=$TRAVIS_BUILD_DIR/contrib/depends/$HOST/lib
 after_script:
     - echo $TRAVIS_COMMIT_RANGE

CMakeLists.txt

@@ -40,6 +40,7 @@ if (IOS)
 endif()
 
 cmake_minimum_required(VERSION 2.8.7)
+message(STATUS "CMake version ${CMAKE_VERSION}")
 
 project(monero)
 
@@ -139,7 +140,6 @@ if(ARCH_ID STREQUAL "ppc64le")
   set(PPC64LE 1)
   set(PPC64   0)
   set(PPC     0)
-
 endif()
 
 if(ARCH_ID STREQUAL "powerpc64" OR ARCH_ID STREQUAL "ppc64")
@@ -517,11 +517,9 @@ if(MSVC)
   include_directories(SYSTEM src/platform/msc)
 else()
   include(TestCXXAcceptsFlag)
-  if (NOT ARM6)
-    if(NOT DEPENDS OR DEPENDS AND NOT ARM)
+  if (NOT ARCH)
     set(ARCH native CACHE STRING "CPU to build for: -march value or 'default' to not pass -march at all")
   endif()
-  endif()
   message(STATUS "Building on ${CMAKE_SYSTEM_PROCESSOR} for ${ARCH}")
   if(ARCH STREQUAL "default")
     set(ARCH_FLAG "")

contrib/depends/toolchain.cmake.in

@@ -51,7 +51,9 @@ if(CMAKE_SYSTEM_NAME STREQUAL "Darwin")
   SET(APPLE True)
   SET(BUILD_TAG "mac-x64")
   SET(BUILD_64 ON)
+  if(NOT TRAVIS)
   SET(ARCH "x86_64")
+  endif()
   SET(BREW OFF)
   SET(PORT OFF)
   SET(CMAKE_OSX_SYSROOT "@sdk@/MacOSX10.11.sdk/")