third_party: Use PIC `Scrt1.o`

When linking code using PIC, `Scrt1.o` is needed instead of `crt1.o`.
This this change uses `Scrt1.o` for all linking.  This appears to work
for both PIC and non-PIC code. Verified by runing all of Pigweed
upstream's Bazel tests.

third_party/debian_stretch_amd64_sysroot.BUILD

diff --git a/third_party/debian_stretch_amd64_sysroot.BUILD b/third_party/debian_stretch_amd64_sysroot.BUILD
index 3dd94fa..0f00dda 100644
--- a/third_party/debian_stretch_amd64_sysroot.BUILD
+++ b/third_party/debian_stretch_amd64_sysroot.BUILD
@@ -19,9 +19,10 @@
 ]
 
 CRT_OBJECTS = [
-    "crt1",
     "crti",
     "crtn",
+    # Use PIC Scrt1.o instead of crt1.o to keep PIC code from segfaulting.
+    "Scrt1",
 ]
 
 [