Override module's C flags when coverage is enabled

Bug: http://b/116873221

Disable -Wframe-larger-than because building without optimization can
make frame larger.  Building dng_sdk with coverage results in a bigger
stack frame than the limit in C flags.

Get optimization level back to -O0 if module has a non-default
optimization level.  Not doing so causes link failures with
libneuralnetworks.so.

Test: Build with coverage.
Change-Id: I36b2979bb6a73023458c8de3241e975845bd36eb
diff --git a/cc/coverage.go b/cc/coverage.go
index 0549705..ad2f1e4 100644
--- a/cc/coverage.go
+++ b/cc/coverage.go
@@ -53,6 +53,10 @@
 		flags.Coverage = true
 		flags.GlobalFlags = append(flags.GlobalFlags, "--coverage", "-O0")
 		cov.linkCoverage = true
+
+		// Override -Wframe-larger-than and non-default optimization
+		// flags that the module may use.
+		flags.CFlags = append(flags.CFlags, "-Wno-frame-larger-than=", "-O0")
 	}
 
 	// Even if we don't have coverage enabled, if any of our object files were compiled