tree-wide: remove Emacs lines from all files This should be handled fine now by .dir-locals.el, so need to carry that stuff in every file.

resolved: apply epoch to system time from PID 1 For use in timesyncd we already defined a compile-time "epoch" value, which is based on the mtime of the NEWS file, and specifies a point in time we know lies in the past at runtime. timesyncd uses this to filter out nonsensical timestamp file data, and bump the system clock to a time that is after the build time of systemd. This patch adds similar bumping code to earliest PID 1 initialization, so that the system never continues operation with a clock that is in the 1970ies or even 1930s.

Use negative_errno() to assert errno is positive after a few system calls This is not particularly intrusive because it happens in simple utility functions. It helps gcc understand that error codes are negative. This gets a rid of most of the remaining warnings.

basic: include only what we use This is a cleaned up result of running iwyu but without forward declarations on src/basic.

util-lib: split out fd-related operations into fd-util.[ch] There are more than enough to deserve their own .c file, hence move them over.

util-lib: split our string related calls from util.[ch] into its own file string-util.[ch] There are more than enough calls doing string manipulations to deserve its own files, hence do something about it. This patch also sorts the #include blocks of all files that needed to be updated, according to the sorting suggestions from CODING_STYLE. Since pretty much every file needs our string manipulation functions this effectively means that most files have sorted #include blocks now. Also touches a few unrelated include files.

build-sys: split internal basic/ library from shared/ basic/ can be used by everything cannot use anything outside of basic/ libsystemd/ can use basic/ cannot use shared/ shared/ can use libsystemd/