Support prebuilt shared libs end with versions

This commit changes how `cc/androidmk.go` generates LOCAL_MODULE_STEM,
LOCAL_MODULE_SUFFIX, and LOCAL_BUILT_MODULE_STEM.  Now, `splitFileExt()`
takes a file name and a list of expected file extensions.
`splitFileExt()` searches the first occurrence of expected file
extensions in the file name.  If it can not find any, it will simply
return the last file extension.

Before this commit, `cc/androidmk.go` simply extracts the last file
extension (e.g. `.so`).  However, if the prebuilt shared libs end with
version numbers (e.g. `libc++.so.1`), it will use `$(LOCAL_MODULE).1` as
LOCAL_BUILT_MODULE_STEM and this will lead to missing target ninja
error.

Bug: 111579848
Test: Build a program that links libc++_host (from prebuilts/clang)
Change-Id: Id96726c69705d518ea725bb6abd8ff4527ca0cbc

cc/util.go

@@ -16,6 +16,7 @@ package cc
 
 import (
 	"fmt"
+	"path/filepath"
 	"regexp"
 	"strings"
 
@@ -102,3 +103,29 @@ func addSuffix(list []string, suffix string) []string {
 	}
 	return list
 }
+
+var shlibVersionPattern = regexp.MustCompile("(?:\\.\\d+)+")
+
+// splitFileExt splits a file name into root, suffix and ext. root stands for the file name without
+// the file extension and the version number (e.g. "libexample"). suffix stands for the
+// concatenation of the file extension and the version number (e.g. ".so.1.0"). ext stands for the
+// file extension after the version numbers are trimmed (e.g. ".so").
+func splitFileExt(name string) (string, string, string) {
+	// Extract and trim the shared lib version number if the file name ends with dot digits.
+	suffix := ""
+	matches := shlibVersionPattern.FindAllStringIndex(name, -1)
+	if len(matches) > 0 {
+		lastMatch := matches[len(matches)-1]
+		if lastMatch[1] == len(name) {
+			suffix = name[lastMatch[0]:lastMatch[1]]
+			name = name[0:lastMatch[0]]
+		}
+	}
+
+	// Extract the file name root and the file extension.
+	ext := filepath.Ext(name)
+	root := strings.TrimSuffix(name, ext)
+	suffix = ext + suffix
+
+	return root, suffix, ext
+}