libgcc6 +universal looks for libquadmath in /opt/local/lib/libgcc/i386

[gnw3]

Updating a Snow Leopard system:

	--->  Scanning binaries for linking errors
	--->  Found 1 broken file, matching files to ports       
	Error: Port libgcc6 is still broken after rebuilding it more than 3 times.

Running port -d -y rev-upgrade revealed the problem:

Could not open /opt/local/lib/libgcc/i386/libquadmath.0.dylib: Error opening or reading file (referenced from /opt/local/lib/libgcc/libgfortran.3.dylib)
	DEBUG: Marking /opt/local/lib/libgcc/libgfortran.3.dylib as broken

As a workaround, I created a symlink in /opt/local/lib/libgcc/i386 to ../libquadmath.0.dylib and was able to install libgcc6. Trivial programs (F90, C, C++) compile in both 32-bt and 64-bit versions:

$ otool -L ./t32-gfortran-mp-6
./t32-gfortran-mp-6:
	/opt/local/lib/libgcc/libgfortran.3.dylib (compatibility version 4.0.0, current version 4.0.0)
	/usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 125.2.11)
	/opt/local/lib/libgcc/libgcc_s.1.dylib (compatibility version 1.0.0, current version 1.0.0)
	/opt/local/lib/libgcc/libquadmath.0.dylib (compatibility version 1.0.0, current version 1.0.0)

[ryandesign (Ryan Carsten Schmidt)]

Duplicate of #54768.