For oracle_fdw. · Pull Request !32 · openGauss/openGauss-server

**What this PR does / why we need it**:
For oracle_fdw. Including oracle_fdw source code(https://github.com/laurenz/oracle_fdw) release 2.2.0 and patch.

**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes #

**Special notes for your reviewer**:
1. To make oracle_fdw, add '--enable-oracle-fdw' when configure. Test with oracle, version 'Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production', use same version for oracle C client library.
2. Patch for oracle_fdw:
a) fix some compiler warning, most are type cast problem
b) since we use g++ as compiler, add "C" in some extern symbol
c) add THR_LOCAL for global var
d) add oracleProcExit to close connection to oracle, called in oracleSession
e) fix input parameter problem for add_path
f) use rte->updatedCols instead of rte->modifiedCols
g) remove '-fPIE' option when compile
h) define WRITE_API and undef OLD_FDW_API for openGauss
i) remove unsupported event for openGauss(SUBXACT_EVENT_PRE_COMMIT_SUB/XACT_EVENT_PRE_COMMIT/XACT_EVENT_PARALLEL_PRE_COMMIT/XACT_EVENT_PRE_PREPARE)
j) use 'type_name' as variable name, since 'typename' is a keyword in c++
3. Some known bugs in oracle_fdw:
a) when execute "EXPLAIN (VERBOSE on) select * from oracle_foreign_table", "ERROR:  bogus varno: 0" reported, seems it's a kernel bug.
b) don't support copy to foreign table.
c) don't support create trigger to foreign table.
d) analyze table will report error: ERROR:  could not open file "base/14790/16392": No such file or directory.
e) can't push down foreign table join stmt to oracle. This feature is added in PG 9.6, so seems it's a normal case.

**Release note**:

```release-note
```

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