configure: add logging

Write compile commands and messages to config.log.
Useful for debugging configure.

configure

@@ -16,15 +16,18 @@ TMPO="${TMPDIR1}/qemu-conf-${RANDOM}-$$-${RANDOM}.o"
 TMPE="${TMPDIR1}/qemu-conf-${RANDOM}-$$-${RANDOM}.exe"
 
 trap "rm -f $TMPC $TMPO $TMPE ; exit" EXIT INT QUIT TERM
+rm -f config.log
 
 compile_object() {
-  $cc $QEMU_CFLAGS -c -o $TMPO $TMPC > /dev/null 2> /dev/null
+  echo $cc $QEMU_CFLAGS -c -o $TMPO $TMPC >> config.log
+  $cc $QEMU_CFLAGS -c -o $TMPO $TMPC >> config.log 2>&1
 }
 
 compile_prog() {
   local_cflags="$1"
   local_ldflags="$2"
-  $cc $QEMU_CFLAGS $local_cflags -o $TMPE $TMPC $LDFLAGS $local_ldflags > /dev/null 2> /dev/null
+  echo $cc $QEMU_CFLAGS $local_cflags -o $TMPE $TMPC $LDFLAGS $local_ldflags >> config.log
+  $cc $QEMU_CFLAGS $local_cflags -o $TMPE $TMPC $LDFLAGS $local_ldflags >> config.log 2>&1
 }
 
 # check whether a command is available to this shell (may be either an