third_party/musl: build PIE/PIC static library

This allows us to then build static-pie binaries.

Change-Id: Ied5c34da85608df0c1b56aec321b9eec367a9615
Reviewed-on: https://review.monogon.dev/c/monogon/+/1837
Reviewed-by: Lorenz Brun <lorenz@monogon.tech>
Tested-by: Jenkins CI
diff --git a/third_party/musl/BUILD.bazel b/third_party/musl/BUILD.bazel
index 1ce390c..e02833c 100644
--- a/third_party/musl/BUILD.bazel
+++ b/third_party/musl/BUILD.bazel
@@ -27,6 +27,7 @@
     cmd = """
     OUT=$$PWD/$(RULEDIR)
     (
+        export CFLAGS="-static-pie -fPIC"
         cd {path}
         ./configure --prefix=$$OUT --syslibdir=$$OUT --libdir=$$OUT
         make -j $$(nproc) install-libs