Closes #5169

Assisted-by: Jay Satiro
Follow-up to 6357a19ff29dac04
Closes #5036

AmiSSL is an Amiga native library which provides a wrapper over OpenSSL.
It also requires all programs using it to use bsdsocket.library
directly, rather than accessing socket functions through clib, which
libcurl was not necessarily doing previously. Configure will now check
for the headers and ensure they are included if found.

Closes #3677

- Add an additional check for LDAP that also checks for OpenSSL since
  on AIX those libraries may be required to link LDAP properly.

Fixes https://github.com/curl/curl/issues/3595
Closes https://github.com/curl/curl/pull/3596

This reverts commit d4f25201fb7da03fc88f90d51101beb3d0026db9.

The overloadable attribute is removed again starting from
NDK17. Actually they only exist in two NDK versions (15 and 16). With
overloadable, the first condition tried will succeed. Results in wrong
detection result.

Closes #3484

Follow-up to #3166 which did the cmake part of this. This type/define is
not used.

Closes #3168

fix a few leftovers

Fixes #3006
Closes #3049

Enable pedantic-errors for GCC >= 5 with --enable-werror. Before GCC 5,
pedantic-errors was synonymous to -Werror=pedantic [0], which is still
the case for clang [1]. With GCC 5, it became complementary [2].

Also fix a resulting error in acinclude.m4 as main's return type was
missing, which is illegal in C99.

[0] https://gcc.gnu.org/onlinedocs/gcc-4.9.0/gcc/Warning-Options.html
[1] https://clang.llvm.org/docs/UsersManual.html#options-to-control-error-and-warning-messages
[2] https://gcc.gnu.org/onlinedocs/gcc-5.1.0/gcc/Warning-Options.html

Closes https://github.com/curl/curl/pull/2747

Since it isn't used either and requires the getnameinfo check

Follow-up to 0aeca41702d2

Closes #2687