Another linux --installer fix

doc/makepanda/makepanda.py

@@ -4674,7 +4674,7 @@ def MakeInstallerLinux():
     if (os.path.exists("/usr/bin/dpkg-deb")):
         oscmd("dpkg --print-architecture > built/tmp/architecture.txt")
     if (os.path.exists("/usr/bin/rpmbuild")):
-        oscmd("rpm -E '%_arch' > built/tmp/architecture.txt")
+        oscmd("rpm -E '%_target_cpu' > built/tmp/architecture.txt")
     ARCH=ReadFile("built/tmp/architecture.txt").strip()
     oscmd("rm -rf linuxroot data.tar.gz control.tar.gz panda3d.spec "+ARCH)
     oscmd("mkdir -p linuxroot/usr/bin")