Add 'openmp' compiler property

Bug: http://b/70692399

If a module has 'openmp: true', add '-fopenmp' to CFlags during any
compile step and pass the libomp runtime to the linker during any link
step.

Test: Build samples in http://aosp/572924
Change-Id: Ic2a6410ec69aae548edaf582ee41659b0058561e

cc/compiler.go

@@ -148,6 +148,9 @@ type BaseCompilerProperties struct {
 
 	// Stores the original list of source files before being cleared by library reuse
 	OriginalSrcs []string `blueprint:"mutated"`
+
+	// Build and link with OpenMP
+	Openmp *bool `android:"arch_variant"`
 }
 
 func NewBaseCompiler() *baseCompiler {
@@ -204,6 +207,10 @@ func (compiler *baseCompiler) compilerDeps(ctx DepsContext, deps Deps) Deps {
 		deps = protoDeps(ctx, deps, &compiler.Proto, Bool(compiler.Properties.Proto.Static))
 	}
 
+	if Bool(compiler.Properties.Openmp) {
+		deps.StaticLibs = append(deps.StaticLibs, "libomp")
+	}
+
 	return deps
 }
 
@@ -494,6 +501,10 @@ func (compiler *baseCompiler) compilerFlags(ctx ModuleContext, flags Flags, deps
 		}
 	}
 
+	if Bool(compiler.Properties.Openmp) {
+		flags.CFlags = append(flags.CFlags, "-fopenmp")
+	}
+
 	return flags
 }