[depends] fix openssl install when INSTALL_PREFIX env var is set

[wsnipex]

Apparently jenkins sets an env var INSTALL_PREFIX, which bleeds into the openssl Makefile, cause someone decided to use $(INSTALL_PREFIX) where everyone else uses $(DESTDIR)....

this PR fixes openssl build and install on all platforms, and addon build on android and linux

overall addon build (still) fails on osx/ios, with this linker error:

[100%] Linking CXX shared library inputstream.rtmp.dylib
/Users/Shared/jenkins/workspace/OSX-64/tools/depends/xbmc-depends/buildtools-native/bin/cmake -E cmake_link_script CMakeFiles/inputstream.rtmp.dir/link.txt --verbose=1
/usr/bin/clang++ -no-cpp-precomp -arch x86_64 -mmacosx-version-min=10.8 -std=c++11 -stdlib=libc++ -g -O2 -std=gnu++11 -g -D_DEBUG -isysroot /Applications/Xcode6.1.1.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.10.sdk -O3 -DNDEBUG -isysroot /Applications/Xcode6.1.1.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.10.sdk -dynamiclib -Wl,-headerpad_max_install_names -Wl,-search_paths_first -arch x86_64 -mmacosx-version-min=10.8 -isysroot /Applications/Xcode6.1.1.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.10.sdk -stdlib=libc++ -compatibility_version 17.0.0 -current_version 1.0.1 -o inputstream.rtmp.1.0.1.dylib -install_name /Users/Shared/jenkins/workspace/OSX-64/tools/depends/target/binary-addons/macosx10.10_x86_64-target/inputstream.rtmp-prefix/src/inputstream.rtmp-build/inputstream.rtmp.17.0.dylib CMakeFiles/inputstream.rtmp.dir/src/RTMPStream.cpp.o /Users/Shared/jenkins/workspace/OSX-64/tools/depends/target/binary-addons/macosx10.10_x86_64-target/build/depends/lib/librtmp.a /Applications/Xcode6.1.1.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.10.sdk/usr/lib/libssl.dylib /Applications/Xcode6.1.1.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.10.sdk/usr/lib/libcrypto.dylib /Users/Shared/jenkins/workspace/OSX-64/tools/depends/target/binary-addons/macosx10.10_x86_64-target/build/depends/lib/libz.a
Undefined symbols for architecture x86_64:
"_netstackdump", referenced from:
_RTMP_Connect1 in librtmp.a(rtmp.o)
_ReadN in librtmp.a(rtmp.o)
_WriteN in librtmp.a(rtmp.o)
_CloseInternal in librtmp.a(rtmp.o)
_RTMPSockBuf_Send in librtmp.a(rtmp.o)
"_netstackdump_read", referenced from:
_ReadN in librtmp.a(rtmp.o)
ld: symbol(s) not found for architecture x86_64

see http://jenkins.kodi.tv/job/OSX-64/9717/consoleText
I don't have time (and hardware) to look into this further, maybe someone else cares enough..
@fetzerch fyi

[notspiff]

prefix, destdir. who cares if those have establishes meanings we do it our way!