vendor: add buildkit

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

vendor/github.com/moby/buildkit/solver/pb/const.go

@@ -0,0 +1,25 @@
+package pb
+
+// InputIndex is incrementing index to the input vertex
+type InputIndex int64
+
+// OutputIndex is incrementing index that another vertex can depend on
+type OutputIndex int64
+
+// RootMount is a base mountpoint
+const RootMount = "/"
+
+// SkipOutput marks a disabled output index
+const SkipOutput OutputIndex = -1
+
+// Empty marks an input with no content
+const Empty InputIndex = -1
+
+// LLBBuilder is a special builder for BuildOp that directly builds LLB
+const LLBBuilder InputIndex = -1
+
+// LLBDefinitionInput marks an input that contains LLB definition for BuildOp
+const LLBDefinitionInput = "buildkit.llb.definition"
+
+// LLBDefaultDefinitionFile is a filename containing the definition in LLBBuilder
+const LLBDefaultDefinitionFile = LLBDefinitionInput