build with 64-bit fsblkcnt_t on 32-bit glibc platforms

It is possible to build with 64-bit file offsets on 32-bit platforms such as
armv7, and indeed this is the default for some build environments such as
Yocto. Use fsblkcnt_t, which is an alias to a type of the correct width, when
computing blockSize.

Author: lhoward

Sources/FoundationEssentials/FileManager/FileManager+Files.swift

@@ -741,8 +741,12 @@ extension _FileManagerImpl {
             let blockSize = UInt64(result.f_bsize)
             #else
             let fsNumber = result.f_fsid
+            #if canImport(Glibc)
+            let blockSize = fsblkcnt_t(result.f_frsize) // support 64-bit block sizes on 32-bit platforms
+            #else
             let blockSize = UInt(result.f_frsize)
             #endif
+            #endif
             var totalSizeBytes = result.f_blocks * blockSize
             var availSizeBytes = result.f_bavail * blockSize
             var totalFiles = result.f_files