Missing x86_64 assembler on mavericks-any way to get it back?

I have a mac mini (intel i7, 2.6 GHz) running OS 10.9.5.

My compiler stopped working last week because apparently the assembler disappeared, and I don't know how that happened or how to fix it. The compiler is gfortran 4.9.2 (from http://hpc.sourceforge.net/) and the error message I get is:

as: assembler (/usr/libexec/gcc/darwin/x86_64/as or /usr/local/libexec/gcc/darwin/x86_64/as) for architecture x86_64 not installed

Installed assemblers are:

/usr/libexec/gcc/darwin/ppc64/as for architecture ppc64

/usr/libexec/gcc/darwin/ppc/as for architecture ppc

/usr/libexec/gcc/darwin/i386/as for architecture i386

/usr/local/libexec/gcc/darwin/m68k/as for architecture m68k

/usr/local/libexec/gcc/darwin/hppa/as for architecture hppa

/usr/local/libexec/gcc/darwin/sparc/as for architecture sparc

/usr/local/libexec/gcc/darwin/m88k/as for architecture m88k

/usr/local/libexec/gcc/darwin/i860/as for architecture i860

I have tried uninstalling and reinstalling gfortran, uninstalling and reinstalling Xcode and the developer tools, and installing gcc 4.9 (also from the hpc binaries) but none of that helped. Does anyone know if there's a way to get the appropriate assembler reinstalled? I know next to nothing about assembly; I'm in a bit over my head here.