kernel/fcall.c optimizations

[ghost]

Features:

• removed duplicated code
• removed noreturn parameter (return_value == NULL when the caller does not want the return value) — less arguments => more opportunities for inlining
• reorganized macros in kernel/fcall.h a bit (for readability)
• removed not used code

Unrelated but required changes:

• fix spurious segfaults in kernel/string.c due to not initialized use_copy
• updated php_phalcon.h in build/
• added missing headers/sources to gen-build.php
• instructed gen-build.php not to strip system headers