The reason for it was that Anders Johansson got this after my previous commit 3c1d3a7 (I think he used 7.4 but I'm not entirely sure):
/bin/sh: command substitution: line 0: syntax error near unexpected token `(' /bin/sh: command substitution: line 0: `uname -s -r -m|sed "s/ /-/g"|tr "[A-Z]" "[a-z]"|tr "/()" "___"'
My patch was sloppy since I didn't really figure out exactly why that happened, but removing the escapes worked for him, and for myself it works either way (which is odd in itself).
You're right $(BUILDDIR) always is used inside ", so they ought to be escaped there. I can't find any difference in this regard between 7.4, 7.6, 7.8 and 7.9 either. I guess I need to look into Anders problem more closely.