Errors when compiling 1.6.4 against PostgreSQL 15 #412

[INFO] Using compiling/linking rules for Linux
In file included from /home/builder/rpmbuild/BUILD/pljava-1_6_4/pljava-so/src/main/c/Backend.c:59:
/home/builder/rpmbuild/BUILD/pljava-1_6_4/pljava-so/src/main/include/pljava/type/String.h:32:25: error: conflicting types for ‘String’
 typedef struct String_* String;
                         ^~~~~~
In file included from /opt/foo/postgres/15/include/server/nodes/parsenodes.h:28,
                 from /opt/foo/postgres/15/include/server/utils/guc.h:16,
                 from /opt/foo/postgres/15/include/server/access/tableam.h:23,
                 from /opt/foo/postgres/15/include/server/commands/trigger.h:16,
                 from /opt/foo/postgres/15/include/server/executor/spi.h:16,
                 from /home/builder/rpmbuild/BUILD/pljava-1_6_4/pljava-so/src/main/c/Backend.c:19:
/opt/foo/postgres/15/include/server/nodes/value.h:61:3: note: previous declaration of ‘String’ was here
 } String;
   ^~~~~~

/home/builder/rpmbuild/BUILD/pljava-1_6_4/pljava-so/src/main/c/type/Type.c: In function ‘TypeClass_alloc2’:
/home/builder/rpmbuild/BUILD/pljava-1_6_4/pljava-so/src/main/c/type/Type.c:1084:26: warning: cast between incompatible function types from ‘void (*)(struct PgObject_ *)’ to ‘jvalue (*)(struct Type_ *, Datum)’ {aka ‘union jvalue (*)(struct Type_ *, long unsigned int)’} [-Wcast-function-type]
  self->coerceDatum     = (DatumCoercer)_PgObject_pureVirtualCalled;
                          ^
/home/builder/rpmbuild/BUILD/pljava-1_6_4/pljava-so/src/main/c/type/Type.c:1085:26: warning: cast between incompatible function types from ‘void (*)(struct PgObject_ *)’ to ‘Datum (*)(struct Type_ *, struct _jobject *)’ {aka ‘long unsigned int (*)(struct Type_ *, struct _jobject *)’} [-Wcast-function-type]
  self->coerceObject    = (ObjectCoercer)_PgObject_pureVirtualCalled;
                          ^
/home/builder/rpmbuild/BUILD/pljava-1_6_4/pljava-so/src/main/c/type/Type.c: In function ‘Type_registerType’:
/home/builder/rpmbuild/BUILD/pljava-1_6_4/pljava-so/src/main/c/type/Type.c:1176:3: warning: cast between incompatible function types from ‘void (*)(struct PgObject_ *)’ to ‘struct Type_ * (*)(Oid)’ {aka ‘struct Type_ * (*)(unsigned int)’} [-Wcast-function-type]
   (TypeObtainer)_PgObject_pureVirtualCalled);
   ^