arm: turn on -Wl,--fatal-warnings

In b238210c0172e771b1302364273016ad1fabafb8, we added
-Wl,--warn-shared-textrel to TARGET_GLOBAL_LDFLAGS. This generated
a warning whenever we created a shared library with a text
relocation.  At the time, we wrote:
=====
Emit a warning when the static linker detects a shared library
has text relocations. Text relocations make it harder to
share pages across processes, and make it harder to use
certain memory protection features in, for example, SELinux.
This warning will turn into an error in a future change
(via --fatal-warnings)
=====

All code which uses text relocations has either been fixed, or
we've temporarily worked around the issue so the code can still
compile.

Enable --fatal-warnings.

This reverts commit 4dc781657b7aa2385cc6ffedc8f3841abdcfd5f6.

Change-Id: I81b96477f1c11069637f28cfd8fb98d42b39be5e
diff --git a/core/combo/TARGET_linux-arm.mk b/core/combo/TARGET_linux-arm.mk
index 854037d..4aa8576 100644
--- a/core/combo/TARGET_linux-arm.mk
+++ b/core/combo/TARGET_linux-arm.mk
@@ -138,6 +138,7 @@
 			-Wl,-z,relro \
 			-Wl,-z,now \
 			-Wl,--warn-shared-textrel \
+			-Wl,--fatal-warnings \
 			-Wl,--icf=safe \
 			$(arch_variant_ldflags)