Set environment variables instead of unsetting them
#!/bin/bash
-unset AS # This makes sure nasm is set as assembler by configure and not GCC.
-unset CFLAGS # default CFLAGS are incompatible with nasm. Set by configure.
+# Use nasm as default assembler. Use relative path here as configure script
+# seems to choke on absolute paths using $CONDA_PREFIX.
+export AS=nasm
+export CFLAGS="" # default CFLAGS are incompatible with nasm.
./autogen.sh
./configure --prefix=${PREFIX}
