Extend compiler cpu optmizations to loongarch64.

This patch extends the just-in-time compiler options in
brian2/codegen/cpp_prefs.py to optimize aggressively on loongarch64
CPU, similarly to numerous other platforms already supported by
brian2.

It was originally published in [Debian bug #1059428] and provided by
Loongson.

[Debian bug #1059428]: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1059428

Signed-off-by: Étienne Mollier <emollier@debian.org>

brian2/codegen/cpp_prefs.py

@@ -124,7 +124,7 @@
             "-mtune=native",
             "-std=c++11",
         ]
-    elif re.match("^(parisc.*|riscv.*|mips.*)$", machine):
+    elif re.match("^(parisc.*|riscv.*|mips.*|loong64.*)$", machine):
         default_buildopts = [
             "-w",
             "-O3",