linux: Add basic Android support

Just needs to disable openat() which doesn't seem allowed
inside APKs by default.

Author: mark-mb

Diff for: config/hwloc.m4

@@ -657,7 +657,8 @@ EOF])
       AC_DEFINE([HWLOC_HAVE_CLZL], [1], [Define to 1 if you have the `clzl' function.])
     ])
 
-    AC_CHECK_FUNCS([openat], [hwloc_have_openat=yes])
+    AS_IF([test "$hwloc_c_vendor" != "android"], [AC_CHECK_FUNCS([openat], [hwloc_have_openat=yes])])
+
 
     AC_CHECK_HEADERS([malloc.h])
     AC_CHECK_FUNCS([getpagesize memalign posix_memalign])

Diff for: config/hwloc_check_vendor.m4

@@ -87,8 +87,13 @@ AC_DEFUN([_HWLOC_CHECK_COMPILER_VENDOR], [
     hwloc_check_compiler_vendor_result="unknown"
 
     # GNU is probably the most common, so check that one as soon as
-    # possible.  Intel pretends to be GNU, so need to check Intel
-    # before checking for GNU.
+    # possible. Intel and Android pretend to be GNU, so need to
+    # check Intel and Android before checking for GNU.
+
+    # Android
+    AS_IF([test "$hwloc_check_compiler_vendor_result" = "unknown"],
+          [HWLOC_IFDEF_IFELSE([__ANDROID__],
+               [hwloc_check_compiler_vendor_result="android"])])
 
     # Intel
     AS_IF([test "$hwloc_check_compiler_vendor_result" = "unknown"],