configure: fix comparing double-digit versions

configure

@@ -612,8 +612,8 @@ def try_check_compiler(cc, lang):
 
   values = (proc.communicate()[0].split() + ['0'] * 7)[0:7]
   is_clang = values[0] == '1'
-  gcc_version = '%s.%s.%s' % tuple(values[1:1+3])
-  clang_version = '%s.%s.%s' % tuple(values[4:4+3])
+  gcc_version = tuple(values[1:1+3])
+  clang_version = tuple(values[4:4+3])
 
   return (True, is_clang, clang_version, gcc_version)
 
@@ -691,6 +691,18 @@ def get_gas_version(cc):
   else:
     return '0'
 
+# Compares (major, min, patch) version tuples
+def less_than(a, b):
+    if a[0] < b[0]:
+        return True
+    elif a[0] == b[0] and a[1] < b[1]:
+        return True
+    elif a[0] == b[0] and a[1] == b[1] and a[2] < b[2]:
+        return True
+    else:
+        return False
+
+
 # Note: Apple clang self-reports as clang 4.2.0 and gcc 4.2.1.  It passes
 # the version check more by accident than anything else but a more rigorous
 # check involves checking the build number against a whitelist.  I'm not
@@ -707,13 +719,13 @@ def check_compiler(o):
   ok, is_clang, clang_version, gcc_version = try_check_compiler(CXX, 'c++')
   if not ok:
     warn('failed to autodetect C++ compiler version (CXX=%s)' % CXX)
-  elif clang_version < '3.4.2' if is_clang else gcc_version < '4.9.4':
+  elif less_than(clang_version, (3, 4, 2)) if is_clang else less_than(gcc_version, (4, 9, 4)):
     warn('C++ compiler too old, need g++ 4.9.4 or clang++ 3.4.2 (CXX=%s)' % CXX)
 
   ok, is_clang, clang_version, gcc_version = try_check_compiler(CC, 'c')
   if not ok:
     warn('failed to autodetect C compiler version (CC=%s)' % CC)
-  elif not is_clang and gcc_version < '4.2.0':
+  elif not is_clang and less_than(gcc_version, (4, 2, 0)):
     # clang 3.2 is a little white lie because any clang version will probably
     # do for the C bits.  However, we might as well encourage people to upgrade
     # to a version that is not completely ancient.