add #include "postgres.h", as required by all .c files

src/backend/executor/execAmi.c

src/backend/executor/execJunk.c

src/backend/executor/execMain.c

src/backend/executor/execProcnode.c

src/backend/executor/execQual.c

src/backend/executor/execScan.c

src/backend/executor/execTuples.c

src/backend/executor/execUtils.c

src/backend/executor/nodeAgg.c

src/backend/executor/nodeAppend.c

src/backend/executor/nodeGroup.c

src/backend/executor/nodeHash.c

src/backend/executor/nodeIndexscan.c

src/backend/executor/nodeMaterial.c

src/backend/executor/nodeMergejoin.c

src/backend/executor/nodeNestloop.c

src/backend/executor/nodeResult.c

src/backend/executor/nodeSeqscan.c

src/backend/executor/nodeSort.c

src/backend/executor/nodeTee.c