Fix floating point conversions

.travis.yml

@@ -190,15 +190,18 @@ jobs:
     - { os: "linux", env: [ "B2_TOOLSET=clang-6.0",   "B2_CXXSTD=14,17"    ], addons: *clang-6   }
     - { os: "linux", env: [ "B2_TOOLSET=clang-7",     "B2_CXXSTD=17"    ], addons: *clang-7   }
     -   os: "linux"
-        env: ["B2_TOOLSET=clang-9", "B2_CXXSTD=17", "B2_CXXFLAGS=-stdlib=libstdc++"]
-        apt:
-          sources:
-            - ubuntu-toolchain-r-test
-            - sourceline: 'deb https://apt.llvm.org/xenial/ llvm-toolchain-xenial-9 main'
-              key_url: 'https://apt.llvm.org/llvm-snapshot.gpg.key'
-        packages:
-          - clang-9
-          
+        env: ["B2_TOOLSET=clang-9", "B2_CXXSTD=11,14,17"]
+        addons:
+          apt:
+            sources:
+              - ubuntu-toolchain-r-test
+              - sourceline: 'deb https://apt.llvm.org/xenial/ llvm-toolchain-xenial-9 main'
+                key_url: 'https://apt.llvm.org/llvm-snapshot.gpg.key'
+            packages:
+              - clang-9
+              - libc6-dbg
+              - libc++-dev
+              - libstdc++-8-dev          
     - { os: "linux", env: [ "B2_TOOLSET=clang-8",     "B2_CXXSTD=17"    ], addons: *clang-8   }
 
     # libc++