ccall: fix vararg count computation (#33123)

(cherry picked from commit a9d4eac)

src/julia-syntax.scm

@@ -938,7 +938,7 @@
           `(block
             ,.(reverse! stmts)
             (foreigncall ,name ,RT (call (core svec) ,@(reverse! T))
-                         ,(if isseq (- (length F) 1) 0) ; 0 or number of arguments before ... in definition
+                         ,(if isseq (- (length atypes) 1) 0) ; 0 or number of arguments before ... in definition
                          ',cconv
                          ,.(reverse! C)
                          ,@GC)) ; GC root ordering is arbitrary

test/ccall.jl

@@ -11,6 +11,17 @@ const libccalltest = "libccalltest"
 const verbose = false
 ccall((:set_verbose, libccalltest), Cvoid, (Int32,), verbose)
 
+@eval function cvarargs()
+    strp = Ref{Ptr{Cchar}}(0)
+    fmt = "%3.1f"
+    len = ccall(:asprintf, Cint, (Ptr{Ptr{Cchar}}, Cstring, Cfloat...), strp, fmt, 0.1)
+    str = unsafe_string(strp[], len)
+    Libc.free(strp[])
+    return str
+end
+@test cvarargs() == "0.1"
+
+
 # test multiple-type vararg handling (there's no syntax for this currently)
 @eval function foreign_varargs()
     strp = Ref{Ptr{Cchar}}(0)
@@ -30,6 +41,7 @@ ccall((:set_verbose, libccalltest), Cvoid, (Int32,), verbose)
 end
 @test foreign_varargs() == "hi+1-2-3-4-5-6-7-8-9-10-11-12-13-14-15-1.1-2.2-3.3-4.4-5.5-6.6-7.7-8.8-9.9\n"
 
+
 # Test for proper argument register truncation
 ccall_test_func(x) = ccall((:testUcharX, libccalltest), Int32, (UInt8,), x % UInt8)
 @test ccall_test_func(3) == 1