[ci] added ubuntu-18.04 to the list of CI targets

.github/workflows/run-tests.yml

@@ -14,7 +14,7 @@ on:
 jobs:
   build:
     name: "Run Unit tests"
-    runs-on: [ubuntu-20.04]
+    runs-on: [ubuntu-20.04, ubuntu-18.04]
     defaults:
       run:
         shell: bash

gef.py

@@ -822,7 +822,7 @@ class GlibcChunk:
         else:
             # Generic case:
             # https://elixir.bootlin.com/glibc/glibc-2.26/source/sysdeps/generic/malloc-alignment.h#L22
-            __alignof__long_double = int(safe_parse_and_eval("_Alignof(long double)"))
+            __alignof__long_double = int(safe_parse_and_eval("_Alignof(long double)") or 0x10)
             malloc_alignment = max(__alignof__long_double, 2 * self.ptrsize)
 
         ceil = lambda n: int(-1 * n // 1 * -1)