Add mechanism to probe for toolchain features

gen.lua

@@ -20,6 +20,7 @@ include 'rules.ninja'
 
 toolchain 'target'
 
+subgen 'probe'
 subgen 'pkg'
 subgen 'src'
 

probe/gen.lua

@@ -0,0 +1,3 @@
+local function probe(var)
+	build('probe', '$outdir/'..var, '$dir/'..var, {var=var})
+end

rules.ninja

@@ -39,6 +39,9 @@ rule mc
 rule muse
   command = muse $museflags -o $out $in
 
+rule probe
+  command = rc ./scripts/probe.rc $var $cc $cflags $ldflags -o /dev/null -x c $in >$out.tmp && mv $out.tmp $out
+
 # misc tools
 rule touch
   command = touch $out

scripts/probe.rc

@@ -0,0 +1,7 @@
+flag e +
+
+var=$1
+shift
+if($* >[2]/dev/null)
+	echo '#define '$var' 1'
+status=()