Minor build warnings should be fixed for a clean build.

[hughbarney]

utf8.c: In function ‘u8_unescape’:
utf8.c:190:22: warning: ‘ch’ may be used uninitialized in this function [-Wmaybe-uninitialized]
dest[0] = (ch>>18) | 0xF0;
^
utf8.c:400:15: note: ‘ch’ was declared here
u_int32_t ch;
^
gcc -O3 -DNDEBUG -Wall -Wno-strict-aliasing -c ios.c -o ios.o
gcc -O3 -DNDEBUG -Wall -Wno-strict-aliasing -c dirpath.c -o dirpath.o
dirpath.c: In function ‘get_cwd’:
dirpath.c:33:11: warning: ignoring return value of ‘getcwd’, declared with attribute warn_unused_result [-Wunused-result]
getcwd(buf, size);