configure: Do not unconditionally add -Wall to host CFLAGS.

Some compilers choke on -Wall, so only add the flag after checking it works.

configure

@@ -1672,7 +1672,7 @@ LIB_INSTALL_EXTRA_CMD='$$(RANLIB) "$(LIBDIR)/$(LIBNAME)"'
 
 CC_O='-o $@'
 
-host_cflags='-D_ISOC99_SOURCE -O3 -g -Wall'
+host_cflags='-D_ISOC99_SOURCE -O3 -g'
 host_libs='-lm'
 
 target_path='$(CURDIR)'
@@ -2334,6 +2334,7 @@ check_cc -D_LARGEFILE_SOURCE <<EOF && add_cppflags -D_LARGEFILE_SOURCE
 EOF
 
 check_host_cflags -std=c99
+check_host_cflags -Wall
 
 case "$arch" in
     alpha|ia64|mips|parisc|sparc)