auto/{cc,options}: Removed unnecessary compiler flags

[BalkanMadman]

The build system should not unconditionally set compilation flag that vary a lot between each user and, as a result, are meant to be toggled individually by distribution/developer/end user.

Among these flags are the options that control program optimisation, debug symbols, the -pipe options and -Werror. -Werror might be harmful since compilers continuously add warnings so the users of new compilers may unexpectedly fail to compile njs since -Werror is set.

The compilation flags should be supplied in the standard CFLAGS environment variable.

Proposed changes

We hit this problem while packaging njs. The build system appends two -O, a -pipe and a -g to CFLAGS even if the user doesn't have these flags in their CFLAGS. I believe, the correct solution is to not unconditionally add any non-warning CFLAGS.

Checklist

Before creating a PR, run through this checklist and mark each as complete:

• I have read the CONTRIBUTING document
• If applicable, I have added tests that prove my fix is effective or that my feature works
• If applicable, I have checked that any relevant tests pass after adding my changes

[xeioex]

@BalkanMadman

NJS follows nginx here. It serves us well. I see no reason to change it without strong arguments.

We hit this problem while packaging njs. The build system appends two -O, a -pipe and a -g to CFLAGS even if the user doesn't have these flags in their CFLAGS.

Normally the last options trump the first ones if they conflict. Does it break anything for you. And if yes, could you, please, share any details? (compilers, OS, CFLAGS)

With CFLAGS, you can still overrule compiler options. See here.
Also, see in our CI pipeline here how options are passed.