Fix build with bash as standard scripting shell

Building with Bash as `/bin/sh` fails:
```
make -j5 VERSION=0.6.10 'XUL_CFLAGS=-I/usr/include/firefox -I/usr/include/nspr' 'XUL_LDFLAGS=-L/usr/lib64/firefox -L/usr/lib64/firefox/sdk/lib 		-lxpcomglue_s -lxul -lmozalloc -lmozsqlite3 -lplds4 -lplc4 		-lnspr4 -lpthread -ldl' XPCOM_ABI_FLAGS=-Wl,-rpath=/usr/lib64/firefox 
CXX="g++" XUL_CFLAGS="-I/usr/include/firefox -I/usr/include/nspr" XUL_LDFLAGS="-L/usr/lib64/firefox -L/usr/lib64/firefox/sdk/lib 		-lxpcomglue_s -lxul -lmozalloc -lmozsqlite3 -lplds4 -lplc4 		-lnspr4 -lpthread -ldl" XPCOM_ABI_FLAGS="-Wl,-rpath=/usr/lib64/firefox" GNOME_CFLAGS="`pkg-config --cflags gnome-keyring-1`" GNOME_LDFLAGS="`pkg-config --libs gnome-keyring-1`" CXXFLAGS="-march=native -O2 -pipe -fomit-frame-pointer -mno-avx -Wall -fno-rtti -fno-exceptions -fPIC -std=gnu++0x -D__STDC_LIMIT_MACROS" LDFLAGS="-Wl,-O1 -Wl,--as-needed " sh config.sh GnomeKeyring.h xpcom_abi.cpp Makefile > config.vars
config.sh: line 17: warning: here-document at line 17 delimited by end-of-file (wanted `EOF')
config.sh: line 16: warning: here-document at line 16 delimited by end-of-file (wanted `EOF')
config.sh: line 18: syntax error near unexpected token `('
make: *** [config.vars] Error 2
```
because of `)` *before* `cat` input.
`)` after `cat` input seems to work with both Dash (Debian/Ubuntu) and Bash (RedHat/Fedora/Gentoo etc)