PR #296: Fix centos 6/7 build.

Change devtoolset for centos 6 and 7 for compilation to work. (to fix #285 )

Signed-off-by: Henner Zeller <h.zeller@acm.org>

GitHub PR #296

Copybara import of the project:

  - e3bf129 (testig) by Henner Zeller <h.zeller@acm.org>
  - 5da6e46 ... more references to devtoolset. by Henner Zeller <h.zeller@acm.org>

Closes #296
fixes #285

PiperOrigin-RevId: 310616568

Docker/docker-generate.sh

@@ -89,8 +89,8 @@ EOF
             cat >> centos-${CENTOS_VERSION}/Dockerfile <<EOF
 # Get a newer GCC version
 RUN yum install -y --nogpgcheck centos-release-scl
-RUN yum install -y --nogpgcheck devtoolset-6
-SHELL [ "scl", "enable", "devtoolset-6" ]
+RUN yum install -y --nogpgcheck devtoolset-7
+SHELL [ "scl", "enable", "devtoolset-7" ]
 
 # Link libstdc++ statically
 ENV BAZEL_LINKOPTS "-static-libstdc++:-lm -static-libstdc++:-lrt"
@@ -122,7 +122,7 @@ EOF
         6)
             cat >> centos-${CENTOS_VERSION}/Dockerfile <<EOF
 RUN yum install -y --nogpgcheck rh-python36
-SHELL [ "scl", "enable", "rh-python36", "devtoolset-6" ]
+SHELL [ "scl", "enable", "rh-python36", "devtoolset-7" ]
 
 RUN python --version
 RUN python3 --version
@@ -134,7 +134,7 @@ RUN cd bazel-2.1.0-dist; ./compile.sh
 RUN cp bazel-2.1.0-dist/output/bazel /usr/local/bin
 RUN bazel --version
 
-SHELL [ "scl", "enable", "devtoolset-6" ]
+SHELL [ "scl", "enable", "devtoolset-7" ]
 EOF
             ;;
         7|8)