Move automake conditionals added by commit d512b25f out of Makefile.inc

Commit d512b25f69 added automake
conditionals to Makefile.inc but since Makefile.inc is included
from Makefile for all other build systems that does not work.

This commit instead adds Makefile.OpenSSL.inc and Makefile.libgcrypt.inc
and moves the automake conditional to its proper place, src/Makefile.am.

The automake conditional includes the correct Makefile.$name.inc per
the crypto library selection/detection done by configure.

All non-autotools build system files in libssh2 are hardcoded to use
OpenSSL and do not get a conditional but at least there is some reuse
because they can all include the new Makefile.OpenSSL.inc.

win32/GNUmakefile

@@ -179,6 +179,9 @@ CFLAGS	+= $(INCLUDES)
 
 vpath %.c . ../src
 
+# only OpenSSL is supported with this build system
+include ../Makefile.OpenSSL.inc
+
 # include Makefile.inc to get CSOURCES define
 include ../Makefile.inc
 

win32/Makefile.Watcom

@@ -93,6 +93,8 @@ LIB_ARG  = $(OBJ_BASE)\stat\wlib.arg
 !ifndef %MAKEFLAGS
 !error You MUST call wmake with the -u switch!
 !else
+# only OpenSSL is supported with this build system
+!include ..\Makefile.OpenSSL.inc
 !include ..\Makefile.inc
 !endif