fix stage0 build issues on host distros with compressed debug sections

distros using bleeding edge binutils default to produce compressed debug
sections, even if debug info was disabled via -g0 in CFLAGS, which leads
to error message like the following as soon as stage0 is built and the
user tries to use the toolchain (e.g., for building stage1):

/lib/gcc/x86_64-unknown-linux-gnu/3.4.6/../../../crti.o:
file not recognized: File format not recognized

or

/bin/ld: /lib/gcc/x86_64-unknown-linux-gnu/3.4.6/../../../crtn.o:
unable to initialize decompress status for section .debug_aranges

more info in this PR: richfelker/musl-cross-make#73

other distros would probably just update to latest binutils to mitigate such
an issue, but this opens pandora's box and leads to a chain of consequences
such that gdb needs to be updated too, newer versions of which now use C++,
etc.
seen from a different PoV, sticking with an older and well-test binutils
version for the time being has the nice effect that binaries produced on
sabotage are way more portable and can be debugged with e.g. a 10 year old
gdb without issues.

KEEP/etc/butch-optflags.sh

@@ -31,6 +31,11 @@ cflags_speed="-O3 -fstrength-reduce -fthread-jumps -fcse-follow-jumps -fcse-skip
 ldflags_base="-Wl,-z,relro,-z,now -Wl,-z,text"
 ldflags_size="-Wl,--gc-sections"
 
+if [ "$STAGE" = 0 ] ; then
+cflags_base="$cflags_base -Wa,--compress-debug-sections=none"
+ldflags_base="$ldflags_base -Wl,--compress-debug-sections=none"
+fi
+
 if [ "$OPT_KEEP_DEBUG" = 1 ] ; then
 	cflags_base="$cflags_base -g"
 else