* src/mcs51/gen.c (genFunction): optimize RECEIVE in reentrant

* src/mcs51/gen.c (genFunction): optimize RECEIVE in reentrant
functions
* src/ds390/gen.c (genFunction, genEndFunction),
* src/ds390/ralloc.c (ds390_assignRegisters),
* src/mcs51/gen.c (genFunction, genEndFunction, mcs51_assignRegisters):
* src/mcs51/ralloc.c (mcs51_assignRegisters): Skip optimizing registers
pushed if there are parameters passed on the stack. Also, a cleaner
way to decide if r0/r1 should be pushed/popped. (Together they fix
bug #918693)

git-svn-id: https://sdcc.svn.sourceforge.net/svnroot/sdcc/trunk/sdcc@3269 4a8a32a2-be11-0410-ad9d-d568d2c75423