Install JIT headers

Hi,

In the standard_planner, we set the proper JIT flags on the resulting
PlannedStmt node. We also offered a planer hook so extensions can
add customized planners. The JIT flags in jit/jit.h however, is
not present on the system. I think it's probably better to
install the jit headers?

diff --git a/src/include/Makefile b/src/include/Makefile
index 6bdfd7db91..041702809e 100644
--- a/src/include/Makefile
+++ b/src/include/Makefile
@@ -19,7 +19,7 @@ all: pg_config.h pg_config_ext.h pg_config_os.h
# Subdirectories containing installable headers
SUBDIRS = access bootstrap catalog commands common datatype \
executor fe_utils foreign \
- lib libpq mb nodes optimizer parser partitioning postmaster \
+ jit lib libpq mb nodes optimizer parser partitioning postmaster \
regex replication rewrite \
statistics storage tcop snowball snowball/libstemmer tsearch \
tsearch/dicts utils port port/atomics port/win32 port/win32_msvc \

Regards,
Donald Dong