It looks like scons has some code to use ${CC}/${CXX}, but it doesn't seem to be working, so in the absence of better ideas he's a "whack it on the head" approach. This at least gets ardour and hydrogen using the correct command to compile and link. OK?
Index: Makefile =================================================================== RCS file: /cvs/ports/devel/scons/Makefile,v retrieving revision 1.26 diff -u -p -r1.26 Makefile --- Makefile 28 Jun 2017 16:26:55 -0000 1.26 +++ Makefile 26 Jul 2017 15:57:36 -0000 @@ -3,6 +3,7 @@ COMMENT= Python-based build system VERSION = 2.5.1 +REVISION = 0 DISTNAME= scons-${VERSION} CATEGORIES= devel Index: patches/patch-engine_SCons_Tool_g++_py =================================================================== RCS file: patches/patch-engine_SCons_Tool_g++_py diff -N patches/patch-engine_SCons_Tool_g++_py --- /dev/null 1 Jan 1970 00:00:00 -0000 +++ patches/patch-engine_SCons_Tool_g++_py 26 Jul 2017 15:57:36 -0000 @@ -0,0 +1,14 @@ +$OpenBSD$ + +Index: engine/SCons/Tool/g++.py +--- engine/SCons/Tool/g++.py.orig ++++ engine/SCons/Tool/g++.py +@@ -44,7 +44,7 @@ import gcc + + cplusplus = __import__('c++', globals(), locals(), []) + +-compilers = ['g++'] ++compilers = ['c++'] + + def generate(env): + """Add Builders and construction variables for g++ to an Environment.""" Index: patches/patch-engine_SCons_Tool_gcc_py =================================================================== RCS file: patches/patch-engine_SCons_Tool_gcc_py diff -N patches/patch-engine_SCons_Tool_gcc_py --- /dev/null 1 Jan 1970 00:00:00 -0000 +++ patches/patch-engine_SCons_Tool_gcc_py 26 Jul 2017 15:57:36 -0000 @@ -0,0 +1,14 @@ +$OpenBSD$ + +Index: engine/SCons/Tool/gcc.py +--- engine/SCons/Tool/gcc.py.orig ++++ engine/SCons/Tool/gcc.py +@@ -40,7 +40,7 @@ import subprocess + + import SCons.Util + +-compilers = ['gcc', 'cc'] ++compilers = ['cc'] + + def generate(env): + """Add Builders and construction variables for gcc to an Environment."""