make the "alternate" clang build use -O0 optimizations

The alternate clang build currently uses strict compilation = false,
this was requested so that we get as many error messages as possible.

We would also like to have an -O0 build run against the unit tests,
as sometimes -O0 will segfault while -O2 won't, etc. So in this
commit the alternate build uses that option also. I also rename
the environment variables, so that the build matrix is based on
casing out whether "alternate_configuration" is true (not strict_
compilation) as previously, and the alternate_configuration flag
leads to options being exported in the before_install phase.

.travis.yml

@@ -3,17 +3,21 @@ compiler:
     - gcc
     - clang
 env:
-    - STRICT_COMPILATION=True
-    - STRICT_COMPILATION=False
+    - ALTERNATE_CONFIGURATION=true
+    - ALTERNATE_CONFIGURATION=false
 matrix:
   exclude:
     - compiler: gcc
-      env: STRICT_COMPILATION=False
+      env: ALTERNATE_CONFIGURATION=false
 before_install:
     - export TARGETS="wesnoth wesnothd campaignd test"
     - export WML_TESTS=true
     - export CPP_TESTS=true
     - export CHECK_UTF8=true
+    - export STRICT_COMPILATION=true
+    - export EXTRA_FLAGS_RELEASE=""
+    - if [ "$ALTERNATE_CONFIGURATION" = true ]; then export STRICT_COMPILATION=false
+    - if [ "$ALTERNATE_CONFIGURATION" = true ]; then export EXTRA_FLAGS_RELEASE="-O0"
     - if [ "$CXX" = "g++" ]; then export TARGETS="wesnoth test"; fi
     - if [ "$CXX" = "g++" ]; then export WML_TESTS=false; fi
 #    - if [ "$CXX" = "g++" ]; then export CPP_TESTS=false; fi
@@ -30,7 +34,7 @@ script:
     - if [ "$CHECK_UTF8" = true ]; then time ./utils/travis/check_utf8.sh; fi
     - time if grep -qorHbm1 "^`echo -ne '\xef\xbb\xbf'`" po/ src/ data/ ; then echo "Error, Found a UTF8 BOM:\n"; grep -orHbm1 "^`echo -ne '\xef\xbb\xbf'`" po/ src/ data/ ; exit 1; fi
 # UTF8 checks are the previous two lines. the second one checks po src data for UTF8 bom, this takes a few seconds.
-    - scons cxxtool=$CXX --debug=time strict=$STRICT_COMPILATION $TARGETS
+    - scons cxxtool=$CXX --debug=time build=release extra_flags_release="$EXRTA_FLAGS_RELEASE" strict=$STRICT_COMPILATION $TARGETS
     - "export DISPLAY=:99.0"
     - "sh -e /etc/init.d/xvfb start"
     - if [[ "$CPP_TESTS" = true ]]; then time ./utils/travis/test_wrapper.sh; fi