build-pkg: add option --brief to "file" command

Option --brief tells "file" not to prepend filenames
to output lines. Using this option is better than parsing
standard format of output of "file" with a regular expression.

Some filenames contain ":". This confuses the regular
expression:

    [build-pkg]     i686-w64-mingw32.static
    Can't get type of file usr/i686-w64-mingw32.static/share/
    gtk-doc/html/libgda-4.0/gen:sql_identifiers.html (libgda).
    file says "usr/i686-w64-mingw32.static/share/gtk-doc/html/
    libgda-4.0/gen:sql_identifiers.html:
    HTML document, ASCII text"

tools/build-pkg.lua

@@ -282,31 +282,25 @@ end
 local function checkFile(file, pkg)
     -- if it is PE32 file, it must have '.exe' in name
     local ext = file:sub(-4):lower()
-    local cmd = 'file --dereference %q'
-    local file_type0 = trim(shell(cmd:format(file)))
-    local file_type = file_type0:match('^[^:]+: (.*)$')
-    if file_type then
-        if ext == '.bin' then
-            -- can be an executable or something else (font)
-        elseif ext == '.exe' then
-            if not file_type:match('PE32') then
-                log('File %s (%s) is %q. Remove .exe',
-                    file, pkg, file_type)
-            end
-        elseif ext == '.dll' then
-            if not file_type:match('PE32.*DLL') then
-                log('File %s (%s) is %q. Remove .dll',
-                    file, pkg, file_type)
-            end
-        else
-            if file_type:match('PE32') then
-                log('File %s (%s) is %q. Add exe or dll',
-                    file, pkg, file_type)
-            end
+    local cmd = 'file --dereference --brief %q'
+    local file_type = trim(shell(cmd:format(file)))
+    if ext == '.bin' then
+        -- can be an executable or something else (font)
+    elseif ext == '.exe' then
+        if not file_type:match('PE32') then
+            log('File %s (%s) is %q. Remove .exe',
+                file, pkg, file_type)
+        end
+    elseif ext == '.dll' then
+        if not file_type:match('PE32.*DLL') then
+            log('File %s (%s) is %q. Remove .dll',
+                file, pkg, file_type)
         end
     else
-        log("Can't get type of file %s (%s). file says %q",
-            file, pkg, file_type0)
+        if file_type:match('PE32') then
+            log('File %s (%s) is %q. Add exe or dll',
+                file, pkg, file_type)
+        end
     end
     for _, t in ipairs(TARGETS) do
         if t ~= target and file:match(t) then