ci: update Travis configuration

 * Drop all versions of gcc < 7 and clang < 5
 * Add clang 11 (development branch)
 * Reenable ASan on Linux with clang 7, the upstream bug has been fixed
 * Drop Xcode 9.2 (macOS 10.12 is no longer supported)
 * Upgrade Xcode 11 to 11.3
 * Workaround issue with missing /usr/local/opt/openssl on macOS
 * Various cleanups

Change-Id: Iee54c0d0480b6ff15bb112a49b3a5c49586ac976
diff --git a/.jenkins.d/10-build.sh b/.jenkins.d/10-build.sh
index cfa32f8..3879bb4 100755
--- a/.jenkins.d/10-build.sh
+++ b/.jenkins.d/10-build.sh
@@ -6,9 +6,8 @@
 
 set -x
 
-git submodule init
 git submodule sync
-git submodule update
+git submodule update --init
 
 if [[ $JOB_NAME == *"code-coverage" ]]; then
     COVERAGE="--with-coverage"
@@ -20,26 +19,26 @@
 sudo_preserve_env PATH -- ./waf --color=yes distclean
 
 if [[ $JOB_NAME != *"code-coverage" && $JOB_NAME != *"limited-build" ]]; then
-  # Configure/build in optimized mode with tests
-  ./waf --color=yes configure --with-tests
-  ./waf --color=yes build -j${WAF_JOBS:-1}
+    # Build in release mode with tests and without precompiled headers
+    ./waf --color=yes configure --with-tests --without-pch
+    ./waf --color=yes build -j$WAF_JOBS
 
-  # Cleanup
-  sudo_preserve_env PATH -- ./waf --color=yes distclean
+    # Cleanup
+    sudo_preserve_env PATH -- ./waf --color=yes distclean
 
-  # Configure/build in optimized mode without tests, but with "other tests"
-  ./waf --color=yes configure --with-other-tests
-  ./waf --color=yes build -j${WAF_JOBS:-1}
+    # Build in release mode without tests, but with "other tests"
+    ./waf --color=yes configure --with-other-tests
+    ./waf --color=yes build -j$WAF_JOBS
 
-  # Cleanup
-  sudo_preserve_env PATH -- ./waf --color=yes distclean
+    # Cleanup
+    sudo_preserve_env PATH -- ./waf --color=yes distclean
 fi
 
-# Configure/build in debug mode with tests and without precompiled headers
-./waf --color=yes configure --debug --with-tests --without-pch $ASAN $COVERAGE
-./waf --color=yes build -j${WAF_JOBS:-1}
+# Build in debug mode with tests
+./waf --color=yes configure --debug --with-tests $ASAN $COVERAGE
+./waf --color=yes build -j$WAF_JOBS
 
-# (tests will be run against debug version)
+# (tests will be run against the debug version)
 
 # Install
 sudo_preserve_env PATH -- ./waf --color=yes install