+tryflag CFLAGS_AUTO -Waddress
+tryflag CFLAGS_AUTO -Warray-bounds
+tryflag CFLAGS_AUTO -Wchar-subscripts
+tryflag CFLAGS_AUTO -Wduplicate-decl-specifier
+tryflag CFLAGS_AUTO -Winit-self
+tryflag CFLAGS_AUTO -Wreturn-type
+tryflag CFLAGS_AUTO -Wsequence-point
+tryflag CFLAGS_AUTO -Wstrict-aliasing
+tryflag CFLAGS_AUTO -Wunused-function
+tryflag CFLAGS_AUTO -Wunused-label
+tryflag CFLAGS_AUTO -Wunused-variable
+fi
+
+# Determine if the compiler produces position-independent code (PIC)
+# by default. If so, we don't need to compile separate object files
+# for libc.a and libc.so.
+if trycppif __PIC__ "$CFLAGS_C99FSE $CPPFLAGS $CFLAGS" ; then
+pic_default=yes
+else
+pic_default=no
+fi
+
+# Reduce space lost to padding for alignment purposes by sorting data
+# objects according to their alignment reqirements. This approximates
+# optimal packing.
+tryldflag LDFLAGS_AUTO -Wl,--sort-section,alignment
+tryldflag LDFLAGS_AUTO -Wl,--sort-common
+
+# When linking shared library, drop dummy weak definitions that were
+# replaced by strong definitions from other translation units.
+tryldflag LDFLAGS_AUTO -Wl,--gc-sections
+
+# Some patched GCC builds have these defaults messed up...
+tryldflag LDFLAGS_AUTO -Wl,--hash-style=both
+
+# Prevent linking if there are undefined symbols; if any exist,
+# libc.so will crash at runtime during relocation processing.
+# The common way this can happen is failure to link the compiler
+# runtime library; implementation error is also a possibility.
+tryldflag LDFLAGS_AUTO -Wl,--no-undefined
+
+# Avoid exporting symbols from compiler runtime libraries. They
+# should be hidden anyway, but some toolchains including old gcc
+# versions built without shared library support and pcc are broken.
+tryldflag LDFLAGS_AUTO -Wl,--exclude-libs=ALL
+
+# Public data symbols must be interposable to allow for copy
+# relocations, but otherwise we want to bind symbols at libc link
+# time to eliminate startup relocations and PLT overhead. Use
+# --dynamic-list rather than -Bsymbolic-functions for greater
+# control over what symbols are left unbound.
+tryldflag LDFLAGS_AUTO -Wl,--dynamic-list="$srcdir/dynamic.list"
+
+# Find compiler runtime library
+test -z "$LIBCC" && tryldflag LIBCC -lgcc && tryldflag LIBCC -lgcc_eh
+test -z "$LIBCC" && tryldflag LIBCC -lcompiler_rt
+test -z "$LIBCC" && try_libcc=`$CC -print-libgcc-file-name 2>/dev/null` \
+ && tryldflag LIBCC "$try_libcc"
+test -z "$LIBCC" && try_libcc=`$CC -print-file-name=libpcc.a 2>/dev/null` \
+ && tryldflag LIBCC "$try_libcc"
+printf "using compiler runtime libraries: %s\n" "$LIBCC"
+
+# Figure out arch variants for archs with variants
+SUBARCH=
+t="$CFLAGS_C99FSE $CPPFLAGS $CFLAGS"
+
+if test "$ARCH" = "i386" ; then
+printf "checking whether compiler can use ebx in PIC asm constraints... "
+cat > "$tmpc" <<EOF
+int foo(int x) { __asm__ ( "" : "+b"(x) ); return x; }
+EOF
+if $CC $CFLAGS_C99FSE $CPPFLAGS $CFLAGS -fPIC \
+ -c -o /dev/null "$tmpc" >/dev/null 2>&1 ; then
+printf "yes\n"
+else
+printf "no\n"
+CFLAGS_AUTO="$CFLAGS_AUTO -DBROKEN_EBX_ASM"
+fi
+fi
+
+if test "$ARCH" = "x86_64" ; then
+trycppif __ILP32__ "$t" && ARCH=x32
+fi
+
+if test "$ARCH" = "arm" ; then
+if trycppif __thumb2__ "$t" ; then
+tryflag CFLAGS_AUTO -mimplicit-it=always
+tryflag CFLAGS_AUTO -Wa,-mimplicit-it=always
+tryflag CFLAGS_AUTO -Wa,-mthumb
+fi
+trycppif __ARMEB__ "$t" && SUBARCH=${SUBARCH}eb
+trycppif __ARM_PCS_VFP "$t" && SUBARCH=${SUBARCH}hf
+# Versions of clang up until at least 3.8 have the wrong constraint codes
+# for floating point operands to inline asm. Detect this so the affected
+# source files can just disable the asm.
+if test "$cc_family" = clang ; then
+printf "checking whether clang's vfp asm constraints work... "
+echo 'float f(float x) { __asm__("":"+t"(x)); return x; }' > "$tmpc"
+if $CC $CFLAGS_C99FSE $CPPFLAGS $CFLAGS -c -o /dev/null "$tmpc" >/dev/null 2>&1 ; then
+printf "yes\n"
+else
+printf "no\n"
+CFLAGS_AUTO="$CFLAGS_AUTO -DBROKEN_VFP_ASM"
+CFLAGS_AUTO="${CFLAGS_AUTO# }"
+fi
+fi