LibC::PtrdiffT is the signed integer type of the result of subtractin…

…g two pointers.

ptrdiff_t is used for pointer arithmetic and array indexing, if negative values are possible.

Refs crystal-lang#823, crystal-lang#4589.

src/lib_c/aarch64-linux-gnu/c/stddef.cr

@@ -1,3 +1,4 @@
 lib LibC
   alias SizeT = ULongLong
+  alias OffsetT = LongLong
 end

src/lib_c/amd64-unknown-openbsd/c/stddef.cr

@@ -1,3 +1,4 @@
 lib LibC
   alias SizeT = ULong
+  alias OffsetT = Long
 end

src/lib_c/arm-linux-gnueabihf/c/stddef.cr

@@ -1,3 +1,4 @@
 lib LibC
   alias SizeT = UInt
+  alias OffsetT = Int
 end

src/lib_c/i686-linux-gnu/c/stddef.cr

@@ -1,3 +1,4 @@
 lib LibC
   alias SizeT = UInt
+  alias OffsetT = Int
 end

src/lib_c/i686-linux-musl/c/stddef.cr

@@ -1,3 +1,4 @@
 lib LibC
   alias SizeT = UInt
+  alias OffsetT = Int
 end

src/lib_c/x86_64-linux-gnu/c/stddef.cr

@@ -1,3 +1,4 @@
 lib LibC
   alias SizeT = ULong
+  alias OffsetT = Long
 end

src/lib_c/x86_64-linux-musl/c/stddef.cr

@@ -1,3 +1,4 @@
 lib LibC
   alias SizeT = ULong
+  alias OffsetT = Long
 end

src/lib_c/x86_64-macosx-darwin/c/stddef.cr

@@ -1,3 +1,4 @@
 lib LibC
   alias SizeT = ULong
+  alias OffsetT = Long
 end

src/lib_c/x86_64-portbld-freebsd/c/stddef.cr

@@ -1,3 +1,4 @@
 lib LibC
   alias SizeT = ULong
+  alias PtrdiffT = Long
 end