gh-93649: Fix dependencies of _testcapi (#94695)

- header files are located in $(srcdir)
- dependencies must not list C files that are also in a makesetup Setup file
- generate SRCDIRS for OOT builds

Makefile.pre.in

@@ -2568,7 +2568,7 @@ MODULE__SHA3_DEPS=$(srcdir)/Modules/_sha3/sha3.c $(srcdir)/Modules/_sha3/sha3.h
 MODULE__SHA512_DEPS=$(srcdir)/Modules/hashlib.h
 MODULE__SOCKET_DEPS=$(srcdir)/Modules/socketmodule.h
 MODULE__SSL_DEPS=$(srcdir)/Modules/_ssl.h $(srcdir)/Modules/_ssl/cert.c $(srcdir)/Modules/_ssl/debughelpers.c $(srcdir)/Modules/_ssl/misc.c $(srcdir)/Modules/_ssl_data.h $(srcdir)/Modules/_ssl_data_111.h $(srcdir)/Modules/_ssl_data_300.h $(srcdir)/Modules/socketmodule.h
-MODULE__TESTCAPI_DEPS=$(srcdir)/Modules/testcapi_long.h Modules/_testcapi/parts.h $(srcdir)/Modules/_testcapi/vectorcall.c
+MODULE__TESTCAPI_DEPS=$(srcdir)/Modules/testcapi_long.h $(srcdir)/Modules/_testcapi/parts.h
 MODULE__SQLITE3_DEPS=$(srcdir)/Modules/_sqlite/connection.h $(srcdir)/Modules/_sqlite/cursor.h $(srcdir)/Modules/_sqlite/microprotocols.h $(srcdir)/Modules/_sqlite/module.h $(srcdir)/Modules/_sqlite/prepare_protocol.h $(srcdir)/Modules/_sqlite/row.h $(srcdir)/Modules/_sqlite/util.h
 
 # IF YOU PUT ANYTHING HERE IT WILL GO AWAY

configure.ac

@@ -6439,6 +6439,7 @@ SRCDIRS="\
   Modules/_sha3 \
   Modules/_sqlite \
   Modules/_sre \
+  Modules/_testcapi \
   Modules/_xxtestfuzz \
   Modules/cjkcodecs \
   Modules/expat \