Copy Bionic's printf/scanf code into sources/android/support.

They were copied from Bionic (as of today), with:

$  cp ~/src/platform_bionic/libc/stdio/{fprintf,fscanf,fvwrite,printf,\
scanf,snprintf,sprintf,sscanf,vasprintf,vfprintf,vfscanf,vprintf,vscanf,\
vsnprintf,vsprintf,vsscanf}.c sources/android/support/src/stdio/
$  cp ~/src/platform_bionic/libc/stdio/{fileext,floatio,fvwrite,local,wcio}.h \
sources/android/support/src/stdio/
$  cp ~/src/platform_bionic/libc/stdlib/strtod.c \
sources/android/support/src/stdio/

As of this commit, these files are unmodified and not built yet.

Change-Id: Ied1d1e4b055df83245a0f0af5635b5950172adab
Add Bionic's printf/scanf implementation files to the build.

The files were added to sources/android/support/src/stdio in the last
commit. This commit adds them to the build. This requires minor changes
to three of the c files, to make them build without the rest of Bionic.

With this commit, printf() (etc) will run the code in
sources/android/support/src/stdio, but the behavior of that function is
still identical to its behavior in Bionic.

Change-Id: I36800b0546877748d0ac6dcfb96ceb44258a6fa1
Merge pull request #17 from awong-dev/hexfloat

Hexfloat