Add Travis CI configuration file for automatic build tests

Github provides a Travis CI integration which makes it easy to have a quick
check of a patch before a pull request is accepted. It is not enough to prove
the correctness of a contribution but at least helps to avoid some of the worst
build problems.

This feature *must* be enabled by the mupen64plus administrator *before this
commit is merged*:

- https://travis-ci.org/profile/mupen64plus
- Login via your Github account
- Make sure you are on "https://travis-ci.org/profile/mupen64plus"
- Switch repository to "On"

.travis.yml

@@ -0,0 +1,22 @@
+language: cpp
+compiler:
+  - gcc
+  - clang
+before_install:
+  - sudo add-apt-repository --yes ppa:zoogie/sdl2-snapshots
+  - sudo apt-get update -qq
+  - sudo apt-get install -y libsdl1.2-dev libsdl2-dev libfreetype6-dev libgl1-mesa-dev libglu1-mesa-dev libpng-dev pkg-config zlib1g-dev liblircclient-dev binutils-dev
+env:
+ - OSD=0
+ - OSD=1
+ - NO_ASM=1
+ - LIRC=1
+ - PROFILE=1
+ - DEBUGGER=1
+ - DBG_CORE=1
+ - DBG_COUNT=1
+ - DBG_COMPARE=1
+ - COUNT_INSTR=1
+script:
+ - make -C projects/unix V=1 clean && CPPFLAGS="-D__extern_always_inline=inline" LDFLAGS="-Wl,--no-add-needed -Wl,--no-undefined" OPTFLAGS="-O2" make SDL_CONFIG=sdl-config CC="${CC}" CXX="${CXX}" -j$(nproc) -C projects/unix V=1 all
+ - make -C projects/unix V=1 clean && CPPFLAGS="-D__extern_always_inline=inline" LDFLAGS="-Wl,--no-add-needed -Wl,--no-undefined" OPTFLAGS="-O2" make SDL_CONFIG=sdl2-config CC="${CC}" CXX="${CXX}" -j$(nproc) -C projects/unix V=1 all