generator: expressions can generate pre-code

generator: expressions can generate pre-code

This patch provides a mechanism for generating
preparatory code for expressions.

This is e.g. necessary when an expression needs computations
which cannot be done in a C-Expression, like for-loops.

This will be used for sumof expressions but may be useful
elsewhere.

Note: Patch 2 of this series has been removed during the review process.

V2: adapt to changes in previous patches

V3: some style and formatting changes according to suggestions from Ran Benita.

Signed-off-by: Christian Linhart <chris@DemoRecorder.com>
Reviewed-by: Ran Benita <ran234@gmail.com>
Message-ID: <54562769.3090405@DemoRecorder.com>
Patch-Thread-Subject: [Xcb] [PATCHSET] ListInputDevices revision 2
Patch-Set: ListInputDevices
Patch-Number: libxcb 3/9
Patch-Version: V3