Update build_style for all templates.

- There's no need to set build_style for custom-install (default).
- gnu_{configure,makefile} renamed to gnu-{configure,makefile}.

srcpkgs/llvm/template

@@ -4,7 +4,7 @@ version=2.9
 distfiles="
 http://www.llvm.org/releases/${version}/llvm-${version}.tgz
 http://www.llvm.org/releases/${version}/clang-${version}.tgz"
-build_style=gnu_configure
+build_style=gnu-configure
 configure_args="--disable-expensive-checks --disable-debug-runtime
 --enable-targets=all --enable-bindings=none --enable-optimize
 --enable-shared --enable-libffi --enable-llvmc-dynamic"