libandroidfw: introduce ExecuteBinary (POSIX only)

Introduce a wrapper around fork and exec.

Test: make libandroidfw_tests
Change-Id: Iff0de5319bb6bb101a3fbef6413dfb4e77198f11
diff --git a/libs/androidfw/Android.bp b/libs/androidfw/Android.bp
index e39926b..172970a 100644
--- a/libs/androidfw/Android.bp
+++ b/libs/androidfw/Android.bp
@@ -48,6 +48,7 @@
         "LocaleData.cpp",
         "misc.cpp",
         "ObbFile.cpp",
+        "PosixUtils.cpp",
         "ResourceTypes.cpp",
         "ResourceUtils.cpp",
         "StreamingZipInflater.cpp",
@@ -152,6 +153,7 @@
             srcs: [
                 "tests/BackupData_test.cpp",
                 "tests/ObbFile_test.cpp",
+                "tests/PosixUtils_test.cpp",
             ],
             shared_libs: common_test_libs + ["libui"],
         },