Without any optimization flags, MSVC does no dead code elimination (DCE) at
all, even for the most trivial cases. DCE is a prerequisite for building libav
correctly, otherwise there are undefined references to functions for other
architectures and disabled components.
-O1 is the minimal optimization flag for MSVC that does include DCE.
_DEPFLAGS='$(CPPFLAGS) $(CFLAGS) -showIncludes -Zs'
_cflags_speed="-O2"
_cflags_size="-O1"
+ _cflags_noopt="-O1"
if $_cc -nologo- 2>&1 | grep -q Linker; then
_ld_o='-out:$@'
else