Most of these are clang specific but I tend to do something like

-pipe

-std=c++11

-gfull # generate correct debugging symbols for dead code stripping

-stdlib=libc++

-Ofast # fast, aggressive optimizations (clang-specific)

-fvectorize # enable loop autovectorizer

-fdiagnostics-show-template-tree (clang: print C++ template error as a tree instead of on a single line)

-Weverything # clang specific: enable every single warning

-Werror

-Wfatal-errors # die after the first error encountered

-Wno-c++98-compat

-Wno-c++98-compat-pedantic

-Wno-global-constructors

-Wno-exit-time-destructors

-ffast-math # enable some floating point optimizations that break IEEE754 compliance but usually work

-funroll-loops # enable loop unrolling

-fstrict-aliasing # make more aggressive assumptions about whether pointers can point to the same objects

-fatal_warnings # treat linker warnings as fatal

-flto # enable link-time optimization

-dead_strip # enable dead code stripping

-Wno-error=deprecated # like being able to put __attribute((deprecated)) in code as a note to self

-Wno-error=#warnings # same thing goes for #warnings