Memory mapped coverage (take 2)

Add a build variable, CLANG_COVERAGE_CONTINUOUS_MODE, instead of
selecting based on paths.

Test: CLANG_COVERAGE_CONTINUOUS_MODE=true m and verify continuous mode works

Change-Id: I731172fc1f00e1cabff8efcf8b99f9a48210b446

rust/coverage.go

@@ -22,6 +22,7 @@ import (
 
 var CovLibraryName = "libprofile-clang-extras"
 
+// Add '%c' to default specifier after we resolve http://b/210012154
 const profileInstrFlag = "-fprofile-instr-generate=/data/misc/trace/clang-%p-%m.profraw"
 
 type coverage struct {
@@ -59,6 +60,10 @@ func (cov *coverage) flags(ctx ModuleContext, flags Flags, deps PathDeps) (Flags
 		flags.LinkFlags = append(flags.LinkFlags,
 			profileInstrFlag, "-g", coverage.OutputFile().Path().String(), "-Wl,--wrap,open")
 		deps.StaticLibs = append(deps.StaticLibs, coverage.OutputFile().Path())
+		if cc.EnableContinuousCoverage(ctx) {
+			flags.RustFlags = append(flags.RustFlags, "-C llvm-args=--runtime-counter-relocation")
+			flags.LinkFlags = append(flags.LinkFlags, "-Wl,-mllvm,-runtime-counter-relocation")
+		}
 	}
 
 	return flags, deps