Add valgrind build bots to CI

This commit adds two build-bots to CI that test the release builds
of jemalloc on linux and macOS under valgrind.

The macOS build is not enabled because valgrind reports
errors about reads of uninitialized memory in some tests and
segfaults in others.

scripts/gen_travis.py

@@ -113,8 +113,28 @@ for combination in unusual_combinations_to_test:
 
 # Development build
 include_rows += '''\
+    # Development build
     - os: linux
       env: CC=gcc CXX=g++ COMPILER_FLAGS="" CONFIGURE_FLAGS="--enable-debug --disable-cache-oblivious --enable-stats --enable-log --enable-prof" EXTRA_CFLAGS="-Werror -Wno-array-bounds"
 '''
 
+# Valgrind build bots
+include_rows += '''
+    # Valgrind
+    - os: linux
+      env: CC=gcc CXX=g++ COMPILER_FLAGS="" CONFIGURE_FLAGS="" EXTRA_CFLAGS="-Werror -Wno-array-bounds" JEMALLOC_TEST_PREFIX="valgrind"
+      addons:
+        apt:
+          packages:
+            - valgrind
+'''
+
+# To enable valgrind on macosx add:
+#
+#  - os: osx
+#    env: CC=gcc CXX=g++ COMPILER_FLAGS="" CONFIGURE_FLAGS="" EXTRA_CFLAGS="-Werror -Wno-array-bounds" JEMALLOC_TEST_PREFIX="valgrind"
+#    install: brew install valgrind
+#
+# It currently fails due to: https://github.com/jemalloc/jemalloc/issues/1274
+
 print travis_template % include_rows