C++: Revert JPL rule changes, keep library change

Author: jbj

cpp/change-notes/2021-09-21-jpl24.md

@@ -1,3 +1,4 @@
 lgtm,codescanning
-* The opt-in queries for JPL C coding standards Rule 24 now exclude macros from
-  system headers.
+* The QL library `semmle.code.cpp.commons.Exclusions` now contains a predicate
+  `isFromSystemMacroDefinition` for identifying code that originates from a
+  macro outside the project being analyzed.

cpp/ql/src/JPL_C/LOC-4/Rule 24/MultipleStmtsPerLine.ql

@@ -10,7 +10,6 @@
  */
 
 import cpp
-import semmle.code.cpp.commons.Exclusions
 
 class OneLineStmt extends Stmt {
   OneLineStmt() {
@@ -35,8 +34,5 @@ where
       other.onLine(f, line) and toMin = other.getLocation().getStartColumn()
     |
       toMin
-    ) and
-  // Exclude statements that are from invocations of system-header macros.
-  // Example: FD_ISSET from glibc.
-  not isFromSystemMacroDefinition(o)
+    )
 select o, "This line contains " + cnt + " statements; only one is allowed."

cpp/ql/src/JPL_C/LOC-4/Rule 24/MultipleVarDeclsPerLine.ql

@@ -10,15 +10,11 @@
  */
 
 import cpp
-import semmle.code.cpp.commons.Exclusions
 
 from DeclStmt d
 where
   exists(Variable v1, Variable v2 | v1 = d.getADeclaration() and v2 = d.getADeclaration() |
     v1 != v2 and
     v1.getLocation().getStartLine() = v2.getLocation().getStartLine()
-  ) and
-  // Exclude declarations that are from invocations of system-header macros.
-  // Example: FD_ZERO from glibc.
-  not isFromSystemMacroDefinition(d)
+  )
 select d, "Multiple variable declarations on the same line."