travis.yml: single-thread build-tcg stages

This still seems to be a problem for Travis.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20200225124710.14152-8-alex.bennee@linaro.org>

.travis.yml

@@ -400,7 +400,7 @@ jobs:
     - name: "GCC check-tcg (some-softmmu)"
       env:
         - CONFIG="--enable-debug-tcg --target-list=xtensa-softmmu,arm-softmmu,aarch64-softmmu,alpha-softmmu"
-        - TEST_BUILD_CMD="make -j${JOBS} build-tcg"
+        - TEST_BUILD_CMD="make build-tcg"
         - TEST_CMD="make check-tcg"
         - CACHE_NAME="${TRAVIS_BRANCH}-linux-gcc-debug-tcg"
 
@@ -409,7 +409,7 @@ jobs:
     - name: "GCC plugins check-tcg (some-softmmu)"
       env:
         - CONFIG="--enable-plugins --enable-debug-tcg --target-list=xtensa-softmmu,arm-softmmu,aarch64-softmmu,alpha-softmmu"
-        - TEST_BUILD_CMD="make -j${JOBS} build-tcg"
+        - TEST_BUILD_CMD="make build-tcg"
         - TEST_CMD="make check-tcg"
         - CACHE_NAME="${TRAVIS_BRANCH}-linux-gcc-debug-tcg"