make "fastcall" symbol private since it doesn't really work in all cases

basis/compiler/tests/alien.factor

@@ -6,6 +6,7 @@ namespaces.private parser quotations sequences
 specialized-arrays stack-checker stack-checker.errors
 system threads tools.test words alien.complex concurrency.promises ;
 FROM: alien.c-types => float short ;
+FROM: alien.private => fastcall ;
 SPECIALIZED-ARRAY: float
 SPECIALIZED-ARRAY: char
 IN: compiler.tests.alien

basis/cpu/x86/32/32.factor

@@ -10,6 +10,7 @@ compiler.cfg.intrinsics compiler.cfg.stack-frame
 cpu.x86.assembler cpu.x86.assembler.operands cpu.x86
 cpu.architecture vm ;
 FROM: layouts => cell ;
+FROM: alien.private => fastcall ;
 IN: cpu.x86.32
 
 M: x86.32 machine-registers

core/alien/alien.factor

@@ -5,7 +5,11 @@ kernel.private byte-arrays byte-vectors arrays init
 continuations.private ;
 IN: alien
 
-SINGLETONS: stdcall thiscall fastcall cdecl mingw ;
+SINGLETONS: stdcall thiscall cdecl mingw ;
+
+<PRIVATE
+SINGLETON: fastcall
+PRIVATE>
 
 UNION: abi stdcall thiscall fastcall cdecl mingw ;