Applied clang-tidy suggestions and export of compile commands for linter support

[Spixmaster]

The export of the compile commands in the CMakeLists.txt, I put them where I think it is fitting. Please adjust how you like if you want to keep.

The changes in the source code are minor. There are still suggestions by clang-tidy left but I programmed the minor ones. Please take especially a look at the headers I added or removed. I do not not whether the place I put them is correct since you support different environments.

The removed ones were not needed. The added ones are needed for the following data types in your source code.

#include <asm-generic/socket.h> //provides SOL_SOCKET, SO_ERROR, SO_PEERCRED, SO_RCVTIMEO, SO_REUSEPORT and 1 more
#include <bits/signum-generic.h> //provides SIGPIPE
#include <cerrno> //provides EAGAIN, EBADF, EINPROGRESS, EINTR, EMFILE and 1 more; preferred in C++ instead of <errno.h>
#include <chrono> //provides duration, duration_cast, microseconds, milliseconds, seconds and 1 more
#include <cstddef> //provides NULL, nullptr_t, size_t
#include <cstdint> //provides int64_t, uint64_t, uint8_t
#include <cstdio> //provides BUFSIZ, snprintf
#include <cstdlib> //provides strtoul, strtoull
#include <ctime> //provides time_t
#include <iterator> //provides advance, distance
#include <limits> //provides numeric_limits
#include <stdexcept> //provides invalid_argument
#include <sys/types.h> //provides ssize_t
#include <vector> //provides vector
#include <bits/types/struct_timeval.h> //provides timeval
#include <type_traits> //provides enable_if, is_array, remove_extent, underlying_type
#include <zconf.h> //provides Bytef, uInt
#include <openssl/asn1.h> //provides ASN1_STRING_get0_data, ASN1_STRING_length
#include <openssl/bio.h> //provides BIO_NOCLOSE, BIO_free_all, BIO_new_mem_buf, BIO_new_socket, BIO_set_nbio
#include <openssl/crypto.h> //provides OPENSSL_INIT_LOAD_CRYPTO_STRINGS
#include <openssl/obj_mac.h> //provides NID_commonName, NID_subject_alt_name
#include <openssl/opensslv.h> //provides OPENSSL_VERSION_NUMBER
#include <openssl/pem.h> //provides PEM_X509_INFO_read_bio
#include <openssl/prov_ssl.h> //provides TLS1_1_VERSION
#include <openssl/safestack.h> //provides STACK_OF
#include <openssl/tls1.h> //provides TLSEXT_NAMETYPE_host_name
#include <openssl/x509.h> //provides X509_INFO_free, X509_NAME_get_text_by_NID, X509_free, X509_get_ext_d2i, X509_get_subject_name and 3 more
#include <openssl/x509_vfy.h> //provides X509_STORE_add_cert, X509_STORE_add_crl, X509_STORE_free, X509_STORE_new, X509_V_OK

The tests succeed like with commit 548dfff. There happend fails and a segmentation fault but like I said that already happened before so these commits probably did not cause them. I probably have not setup the tests correctly.

[yhirose]

@Spixmaster thanks for the pull request, but I am not going to merge it with the same reason as #1297, #1708,
#1776. Thanks for your understanding. :)

[Spixmaster]

@yhirose I think that at least the missing headers should be included.

[Spixmaster]

@yhirose I do not mind that you decline this pull request but apply at least some of the fixes. Headers are missing and some variables can be declared const.