Disallow redefinition of section symbols.

Differential Revision: https://reviews.llvm.org/D30235

llvm-svn: 296180
diff --git a/llvm/test/MC/ELF/section-sym-err.s b/llvm/test/MC/ELF/section-sym-err.s
new file mode 100644
index 0000000..789fee7
--- /dev/null
+++ b/llvm/test/MC/ELF/section-sym-err.s
@@ -0,0 +1,6 @@
+// RUN: not llvm-mc -filetype=obj -triple x86_64-pc-linux-gnu %s -o %t.o 2>&1 | FileCheck %s
+
+.section foo
+foo:
+
+// CHECK: error: invalid symbol redefinition