Merging minor security fix (#318)

The function `SET_OF__encode_sorted` stored the working element buffer
in a static variable. If called recursively (that is, when performing
encoding of a SET containing another SET) the outermost element buffer
is therefore clobbered by the innermost call.

This causes a SEGV on continuation of the outermost call.

Bug found during testing of [https://github.com/surevine/spiffing Spiffing],
fix verified with the same test suite.

zeroed repeat. Fix takes value of repeat.

Add aper encoder for SET_OF

similar fix for OCTET STRING)

Add EXTERNAL support

- Remove EXTERNAL from asn1p_l.l and asn1p_y.y
- Add EXTERNAL ASN.1 definition from ITU-T X.208 in
  skeletons/standard-modules/ASN1C-UsefulInformationObjectClasses.asn1
- Add a test case:
  tests/tests-asn1c-compiler/159-EXTERNAL-OK.asn1
  tests/tests-c-compiler/check-src/check-159.c
- Regenerate all tests/tests-asn1c-compiler/*.asn1.* files

Remove asn1p_l.c, asn1p_y.c and asn1_p.h from the repository.
https://www.gnu.org/software/automake/manual/html_node/Yacc-and-Lex.html
https://www.gnu.org/software/automake/manual/html_node/Built-Sources-Example.html#Built-Sources-Example

The function `SET_OF__encode_sorted` stored the working element buffer
in a static variable. If called recursively (that is, when performing
encoding of a SET containing another SET) the outermost element buffer
is therefore clobbered by the innermost call.

This causes a SEGV on continuation of the outermost call.

Bug found during testing of [https://github.com/surevine/spiffing Spiffing],
fix verified with the same test suite.

in calculations when gmtoff was not initialized before first use

Mimic what OAI's asnfix.c of generate_asn1 script does.

Mimic what OAI's asnfix.c of generate_asn1 script does.

asn1c_save.c:238:5: error: this ‘for’ clause does not guard... [-Werror=misleading-indentation]
     for(int i = 0; i < argc; i++)
     ^~~
asn1c_save.c:240:2: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the ‘for’
  safe_fprintf(mkf, "\n\n");
  ^~~~~~~~~~~~

../skeletons/INTEGER.c:510:60: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
             if(specs && specs->field_unsigned && dec_value <= ULONG_MAX) {

This fixes the following undefined behaviour

converter-example.c:721:13: runtime error: null pointer passed as argument 2, which is declared to never be null
/usr/include/string.h:44:28: note: nonnull attribute specified here

Previously some uper_* function were called