Update to Boogie 2.15.9 (#441)

Author: gauravpartha

.github/workflows/ci.yml

@@ -14,7 +14,7 @@ jobs:
     container: gobraverifier/gobra-base:v5_z3_4.8.7 # Thank you, Gobra team
     env:
       BOOGIE_EXE: "boogie/Boogie"
-      LINUX_BOOGIE_URL: "https://github.com/viperproject/boogie-builder/releases/download/bae82d3a7b383161/boogie-linux.zip"
+      LINUX_BOOGIE_URL: "https://github.com/viperproject/boogie-builder/releases/download/7449a7a899c02c95/boogie-linux.zip"
     steps:
     - name: Checkout Carbon
       uses: actions/checkout@v2
@@ -57,6 +57,7 @@ jobs:
         unzip boogie-linux.zip
         rm -rf boogie-linux.zip
         mv binaries-linux boogie
+        boogie/Boogie /version
         pwd
 
     - name: Test Carbon

src/main/scala/viper/carbon/boogie/BoogieNameGenerator.scala

@@ -19,7 +19,7 @@ class BoogieNameGenerator extends DefaultNameGenerator {
     "invariant", "goto", "break", "return", "call", "forall", "assert", "havoc", "assume", "returns", "var", "implementation",
     "axiom", "exists", "old", "false", "real", "int", "true", "bool", "finite", "ensures", "requires", "modifies", "where", "par", "lambda",
     "uses", "RTP", "RTZ", "yield", "async", "roundNearestTiesToAway", "roundNearestTiesToEven", "extends", "roundTowardPositive",
-    "roundTowardZero", "RNA", "RTN", "roundTowardNegative", "RNE") ++
+    "roundTowardZero", "RNA", "RTN", "roundTowardNegative", "RNE", "is") ++
     Set("Set", "MultiSet", "Seq")
   val SMTreservedNames: Set[String] = Set(
     // Basic symbols: