make command line parsing more compliant with configure script

- generic --* options are defined to be booleans, without the
  possibility of having an additional parameter
- -qt and -system options don't exist in the --* form
- --foo=bar options exist only in the --* form

Task-number: QTBUG-55610
Change-Id: Ib0480ac6f479df48045c9de8e854a525862ee363
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

config_help.txt

@@ -46,7 +46,7 @@ Conventions for the remaining options: When an option's description is
 followed by a list of values in brackets, the interpretation is as follows:
 'yes' represents the bare option; all other values are possible prefixes to
 the option, e.g., -no-gui. Alternatively, the value can be assigned, e.g.,
--gui=yes. Values are listed in the order they are tried if not specified;
+--gui=yes. Values are listed in the order they are tried if not specified;
 'auto' is a shorthand for 'yes/no'. Solitary 'yes' and 'no' represent binary
 options without auto-detection.
 

mkspecs/features/qt_configure.prf

@@ -245,17 +245,20 @@ defineTest(qtConfParseCommandLine) {
         } else: contains(c, "^--?(disable|no)-(.*)") {
             opt = $$replace(c, "^--?(disable|no)-(.*)", "\\2")
             val = no
-        } else: contains(c, "^--?qt-(.*)") {
-            opt = $$replace(c, "^--?qt-(.*)", "\\1")
+        } else: contains(c, "^--([^=]+)=(.*)") {
+            opt = $$replace(c, "^--?([^=]+)=(.*)", "\\1")
+            val = $$replace(c, "^--?([^=]+)=(.*)", "\\2")
+        } else: contains(c, "^--(.*)") {
+            opt = $$replace(c, "^--(.*)", "\\1")
+            val = yes
+        } else: contains(c, "^-qt-(.*)") {
+            opt = $$replace(c, "^-qt-(.*)", "\\1")
             val = qt
-        } else: contains(c, "^--?system-(.*)") {
-            opt = $$replace(c, "^--?system-(.*)", "\\1")
+        } else: contains(c, "^-system-(.*)") {
+            opt = $$replace(c, "^-system-(.*)", "\\1")
             val = system
-        } else: contains(c, "^--?([^-].*)=(.*)") {
-            opt = $$replace(c, "^--?([^-].*)=(.*)", "\\1")
-            val = $$replace(c, "^--?([^-].*)=(.*)", "\\2")
-        } else: contains(c, "^--?([^-].*)") {
-            opt = $$replace(c, "^--?([^-].*)", "\\1")
+        } else: contains(c, "^-(.*)") {
+            opt = $$replace(c, "^-(.*)", "\\1")
             val =
         } else {
             qtConfAddError("Invalid command line parameter '$$c'.")