Suppress warnings with GCC 4.9.0

Warnings:

    % gcc recipe.c -o recipe
    recipe.c: In function ‘destroy_RecipeList’:
    recipe.c:43:3: error: ‘for’ loop initial declarations are only allowed in C99 or C11 mode
       for (int i = 0; i < list->size; i++) {
       ^
    recipe.c:43:3: note: use option -std=c99, -std=gnu99, -std=c11 or -std=gnu11 to compile your code
    recipe.c: In function ‘add_recipe_to_RecipeList’:
    recipe.c:54:3: error: ‘for’ loop initial declarations are only allowed in C99 or C11 mode
       for (int i = 0; i < list->size; i++) {
       ^
    recipe.c: In function ‘print_RecipeList’:
    recipe.c:89:3: error: ‘for’ loop initial declarations are only allowed in C99 or C11 mode
       for (int i = 0; i < list->size; i++) {
       ^
    recipe.c: In function ‘print_target_recipe_RecipeList’:
    recipe.c:95:3: error: ‘for’ loop initial declarations are only allowed in C99 or C11 mode
       for (int i = 0; i < list->size; i++) {
       ^

GCC version:

    % gcc -v
    Using built-in specs.
    COLLECT_GCC=gcc
    COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/4.9/lto-wrapper
    Target: x86_64-linux-gnu
    Configured with: ../src/configure -v --with-pkgversion='Debian 4.9.0-10' --with-bugurl=file:///usr/share/doc/gcc-4.9/README.Bugs --enable-languages=c,c++,java,go,d,fortran,objc,obj-c++ --prefix=/usr --program-suffix=-4.9 --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.9 --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --enable-gnu-unique-object --disable-libmudflap --disable-vtable-verify --enable-plugin --with-system-zlib --disable-browser-plugin --enable-java-awt=gtk --enable-gtk-cairo --with-java-home=/usr/lib/jvm/java-1.5.0-gcj-4.9-amd64/jre --enable-java-home --with-jvm-root-dir=/usr/lib/jvm/java-1.5.0-gcj-4.9-amd64 --with-jvm-jar-dir=/usr/lib/jvm-exports/java-1.5.0-gcj-4.9-amd64 --with-arch-directory=amd64 --with-ecj-jar=/usr/share/java/eclipse-ecj.jar --enable-objc-gc --enable-multiarch --with-arch-32=i586 --with-abi=m64 --with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
    Thread model: posix
    gcc version 4.9.0 (Debian 4.9.0-10)
Merge pull request #1 from kou/suppress-warnings

Suppress warnings with GCC 4.9.0