Add iOS CMake build to Travis CI

Use the following CMake flags:
-DCMAKE_SYSTEM_NAME=iOS - for specifying it is an iOS build
-DCMAKE_FIND_ROOT_PATH=/usr/local - dir to search for the built wxWidgets libraries
-DCMAKE_XCODE_ATTRIBUTE_CODE_SIGNING_ALLOWED=NO - don't require signing app packages
-DCMAKE_OSX_DEPLOYMENT_TARGET=10.12 - specify a target so both the libraries and sample will use the same architecture

Also use the code signing flag when testing precompiled header support.
Don't build the default samples, widgets sample has features that are not supported by the iOS build.

Xcode seems to rebuild the libraries when installing, so call CMake only once.

build/tools/travis-ci.sh

@@ -11,6 +11,7 @@ wxBUILD_ARGS="-j$wxPROC_COUNT"
 case $wxTOOLSET in
     cmake)
         if [ -z $wxCMAKE_TESTS ]; then wxCMAKE_TESTS=CONSOLE_ONLY; fi
+        if [ -z $wxCMAKE_SAMPLES ]; then wxCMAKE_SAMPLES=SOME; fi
         if [ "$wxCMAKE_GENERATOR" == "Xcode" ]; then
             wxBUILD_ARGS="-jobs $wxPROC_COUNT -quiet"
         fi
@@ -20,13 +21,22 @@ case $wxTOOLSET in
         echo 'Configuring...'
         mkdir build_cmake
         pushd build_cmake
-        cmake -G "$wxCMAKE_GENERATOR" $wxCMAKE_DEFINES -D wxBUILD_SAMPLES=SOME -D wxBUILD_TESTS=$wxCMAKE_TESTS ..
+        cmake -G "$wxCMAKE_GENERATOR" $wxCMAKE_DEFINES -D wxBUILD_SAMPLES=$wxCMAKE_SAMPLES -D wxBUILD_TESTS=$wxCMAKE_TESTS ..
         echo 'travis_fold:end:configure'
 
-        echo 'travis_fold:start:building'
-        echo 'Building...'
-        cmake --build . -- $wxBUILD_ARGS
-        echo 'travis_fold:end:building'
+        if [ "$wxCMAKE_GENERATOR" != "Xcode" ]; then
+            echo 'travis_fold:start:building'
+            echo 'Building...'
+            cmake --build . -- $wxBUILD_ARGS
+            echo 'travis_fold:end:building'
+        fi
+
+        echo 'travis_fold:start:install'
+        if [ "$wxCMAKE_GENERATOR" == "Xcode" ]; then echo -n 'Building and '; fi
+        echo 'Installing...'
+        sudo env "PATH=$PATH" cmake --build . --target install -- $wxBUILD_ARGS
+        popd
+        echo 'travis_fold:end:install'
 
         if [ "$wxCMAKE_TESTS" != "OFF" ]; then
             echo 'travis_fold:start:testing'
@@ -35,12 +45,6 @@ case $wxTOOLSET in
             echo 'travis_fold:end:testing'
         fi
 
-        echo 'travis_fold:start:install'
-        echo 'Installing...'
-        sudo env "PATH=$PATH" cmake --build . --target install -- $wxBUILD_ARGS
-        popd
-        echo 'travis_fold:end:install'
-
         echo 'travis_fold:start:testinstall'
         echo 'Testing installation...'
         mkdir build_cmake_install_test