[Data] Fix build issue with Static SDK for Linux. (#1293)

Musl's definition of `S_IFMT` gets imported by the Swift importer, which
means Swift can see `S_IFMT` as a `CInt` and also `S_IFMT` from the Swift
overlay as a `mode_t`.  The upshot is that attempting to convert it to
`mode_t` produces an ambiguity error, as Swift doesn't know which
definition to use.

rdar://147201087

Author: al45tair

Sources/FoundationEssentials/Data/Data+Reading.swift

@@ -336,7 +336,7 @@ internal func readBytesFromFile(path inPath: PathOrURL, reportProgress: Bool, ma
     }
 
     let fileSize = min(Int(clamping: filestat.st_size), maxLength ?? Int.max)
-    let fileType = mode_t(filestat.st_mode) & mode_t(S_IFMT)
+    let fileType = mode_t(filestat.st_mode) & S_IFMT
 #if !NO_FILESYSTEM
     let shouldMap = shouldMapFileDescriptor(fd, path: inPath, options: options)
 #else