Just setting HEADER_SEARCH_PATHS doesn't work for me.
Anyway the error is not happening during the pre-compile stage (when it searches for headers) but when its compiling addons/ofxOsc/libs/oscpack/src/ip/posix/UdpSocket.cpp.
that file includes "ip/UdpSocket.h" and assumes that its grandparent folder is on the path. Not the header search paths, but the -I paths passed to compile
consequently, addons/ofxOsc/libs/oscpack/src/ is not included in the call to the compiler:
CompileC /Users/crucial/Library/Developer/Xcode/DerivedData/PlaySPLOM-gwpsbmgveykcqsheakzuilcqldtb/Build/Intermediates/PlaySPLOM.build/Debug/PlaySPLOM.build/Objects-normal/x86_64/UdpSocket.o /Users/crucial/code/idmx/of_v20151008_osx_release/addons/ofxOsc/libs/oscpack/src/ip/posix/UdpSocket.cpp normal x86_64 c++ com.apple.compilers.llvm.clang.1_0.compiler
cd /Users/crucial/code/idmx/of_v20151008_osx_release/apps/myApps/PlaySPLOM
export LANG=en_US.US-ASCII
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang -x c++ -arch x86_64 -fmessage-length=0 -fdiagnostics-show-note-include-stack -fmacro-backtrace-limit=0 -std=c++11 -stdlib=libc++ -Wno-trigraphs -fpascal-strings -O0 -Wno-missing-field-initializers -Wno-missing-prototypes -Wno-return-type -Wno-non-virtual-dtor -Wno-overloaded-virtual -Wno-exit-time-destructors -Wno-missing-braces -Wparentheses -Wswitch -Wno-unused-function -Wno-unused-label -Wno-unused-parameter -Wno-unused-variable -Wno-unused-value -Wno-empty-body -Wno-uninitialized -Wno-unknown-pragmas -Wno-shadow -Wno-four-char-constants -Wno-conversion -Wno-constant-conversion -Wno-int-conversion -Wno-bool-conversion -Wno-enum-conversion -Wno-shorten-64-to-32 -Wno-newline-eof -Wno-c++11-extensions -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.11.sdk -fasm-blocks -fstrict-aliasing -Wdeprecated-declarations -Wno-invalid-offsetof -mmacosx-version-min=10.7 -g -mssse3 -Wno-sign-conversion -I/Users/crucial/Library/Developer/Xcode/DerivedData/PlaySPLOM-gwpsbmgveykcqsheakzuilcqldtb/Build/Intermediates/PlaySPLOM.build/Debug/PlaySPLOM.build/PlaySPLOMDebug.hmap -I/Users/crucial/code/idmx/of_v20151008_osx_release/apps/myApps/PlaySPLOM/bin/include -I../../../libs/openFrameworks -I../../../libs/openFrameworks/.settings -I../../../libs/openFrameworks/3d -I../../../libs/openFrameworks/app -I../../../libs/openFrameworks/communication -I../../../libs/openFrameworks/events -I../../../libs/openFrameworks/gl -I../../../libs/openFrameworks/graphics -I../../../libs/openFrameworks/math -I../../../libs/openFrameworks/sound -I../../../libs/openFrameworks/types -I../../../libs/openFrameworks/utils -I../../../libs/openFrameworks/video -I../../../libs/poco/include -I../../../libs/freetype/include -I../../../libs/freetype/include/freetype2 -I../../../libs/fmodex/include -I../../../libs/glew/include -I../../../libs/FreeImage/include -I../../../libs/tess2/include -I../../../libs/cairo/include/cairo -I../../../libs/rtAudio/include -I../../../libs/glfw/include -I../../../libs/boost/include -I../../../libs/utf8cpp/include -I../../../libs/openssl/include -Isrc -I/Users/crucial/Library/Developer/Xcode/DerivedData/PlaySPLOM-gwpsbmgveykcqsheakzuilcqldtb/Build/Intermediates/PlaySPLOM.build/Debug/PlaySPLOM.build/DerivedSources/x86_64 -I/Users/crucial/Library/Developer/Xcode/DerivedData/PlaySPLOM-gwpsbmgveykcqsheakzuilcqldtb/Build/Intermediates/PlaySPLOM.build/Debug/PlaySPLOM.build/DerivedSources -F/Users/crucial/code/idmx/of_v20151008_osx_release/apps/myApps/PlaySPLOM/bin -F/Users/crucial/code/idmx/of_v20151008_osx_release/apps/myApps/PlaySPLOM/../../../libs/glut/lib/osx -D__MACOSX_CORE__ -mtune=native -MMD -MT dependencies -MF /Users/crucial/Library/Developer/Xcode/DerivedData/PlaySPLOM-gwpsbmgveykcqsheakzuilcqldtb/Build/Intermediates/PlaySPLOM.build/Debug/PlaySPLOM.build/Objects-normal/x86_64/UdpSocket.d --serialize-diagnostics /Users/crucial/Library/Developer/Xcode/DerivedData/PlaySPLOM-gwpsbmgveykcqsheakzuilcqldtb/Build/Intermediates/PlaySPLOM.build/Debug/PlaySPLOM.build/Objects-normal/x86_64/UdpSocket.dia -c /Users/crucial/code/idmx/of_v20151008_osx_release/addons/ofxOsc/libs/oscpack/src/ip/posix/UdpSocket.cpp -o /Users/crucial/Library/Developer/Xcode/DerivedData/PlaySPLOM-gwpsbmgveykcqsheakzuilcqldtb/Build/Intermediates/PlaySPLOM.build/Debug/PlaySPLOM.build/Objects-normal/x86_64/UdpSocket.o
/Users/crucial/code/idmx/of_v20151008_osx_release/addons/ofxOsc/libs/oscpack/src/ip/posix/UdpSocket.cpp:37:10: fatal error: 'ip/UdpSocket.h' file not found
#include "ip/UdpSocket.h"
^
1 error generated.I'm on nightly 9 : of_v20151008_osx_release
I added ofxOsc using the XCode plugin. This is probably what doesn't work properly.
I never figured out how to add an addon by using addons.make That seems to be just for linux, not OS X.
This isn't explained at all here: http://www.ofxaddons.com/pages/howto