travis: Switch to i386 version toolchain for x86

Currently this uses x86_64 version toolchain for x86 build in
travis-ci. Change it to i386 version to avoid updating the
buildman toolchain path every time when the toolchain version
number is changed, eg: from 7.3.0 to 8.1.0.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>

.travis.yml

@@ -68,9 +68,9 @@ before_script:
   - if [[ "${TOOLCHAIN}" == *microblaze* ]]; then ./tools/buildman/buildman --fetch-arch microblaze ; fi
   - if [[ "${TOOLCHAIN}" == *mips* ]]; then ./tools/buildman/buildman --fetch-arch mips ; fi
   - if [[ "${TOOLCHAIN}" == *sh* ]]; then ./tools/buildman/buildman --fetch-arch sh2 ; fi
-  - if [[ "${TOOLCHAIN}" == *x86_64* ]]; then
-      ./tools/buildman/buildman --fetch-arch x86_64;
-      echo -e "\n[toolchain-prefix]\nx86 = ${HOME}/.buildman-toolchains/gcc-7.3.0-nolibc/x86_64-linux/bin/x86_64-linux-" >> ~/.buildman;
+  - if [[ "${TOOLCHAIN}" == *i386* ]]; then
+      ./tools/buildman/buildman --fetch-arch i386;
+      echo -e "\n[toolchain-alias]\nx86 = i386" >> ~/.buildman;
     fi
   - if [[ "${TOOLCHAIN}" == arc ]]; then
        wget https://github.com/foss-for-synopsys-dwc-arc-processors/toolchain/releases/download/arc-2017.09-release/arc_gnu_2017.09_prebuilt_uclibc_le_archs_linux_install.tar.gz &&
@@ -208,7 +208,7 @@ matrix:
     - name: "buildman sandbox x86"
       env:
         - BUILDMAN="sandbox x86"
-          TOOLCHAIN="x86_64"
+          TOOLCHAIN="i386"
     - name: "buildman kirkwood (excluding openrd)"
       env:
         - BUILDMAN="kirkwood -x openrd"
@@ -321,19 +321,19 @@ matrix:
       env:
         - TEST_PY_BD="sandbox"
           BUILDMAN="^sandbox$"
-          TOOLCHAIN="x86_64"
+          TOOLCHAIN="i386"
     - name: "test/py sandbox_spl"
       env:
         - TEST_PY_BD="sandbox_spl"
           TEST_PY_TEST_SPEC="test_ofplatdata"
           BUILDMAN="^sandbox$"
-          TOOLCHAIN="x86_64"
+          TOOLCHAIN="i386"
           TEST_PY_TOOLS="yes"
     - name: "test/py sandbox_flattree"
       env:
         - TEST_PY_BD="sandbox_flattree"
           BUILDMAN="^sandbox_flattree$"
-          TOOLCHAIN="x86_64"
+          TOOLCHAIN="i386"
     - name: "test/py vexpress_ca15_tc2"
       env:
         - TEST_PY_BD="vexpress_ca15_tc2"
@@ -406,7 +406,7 @@ matrix:
           TEST_PY_TEST_SPEC="not sleep"
           QEMU_TARGET="i386-softmmu"
           BUILDMAN="^qemu-x86$"
-          TOOLCHAIN="x86_64"
+          TOOLCHAIN="i386"
           BUILD_ROM="yes"
     - name: "test/py zynq_zc702"
       env: