deskutils/taskwarrior: Fix i386 build and WITH_DEBUG builds

• Cast to time_t in Datetime::operator+/- (libshared): time_t is 32-bit on i386, so the braced return narrowed int64_t and clang rejected it with -Wc++11-narrowing. Only needed on 32-bit architectures, so apply the patch through EXTRA_PATCHES when ARCH is i386 instead of always.
• Stop upstream from compiling -DTASK_TEST_RCDIR="${CMAKE_SOURCE_DIR}/doc/rc" into the binary for Debug builds: WITH_DEBUG made the binary write "include <WRKSRC>/doc/rc/default.theme" into every generated .taskrc, breaking it once the work directory is removed. Also drop the ineffective -DCMAKE_BUILD_TYPE=release (Uses/cmake.mk appends its own CMAKE_BUILD_TYPE afterwards, which always wins).