[PATCH] travis-ci: Use clang-10 for the [s390x] Clang (disable-tcg) job

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On Ubuntu Bionic 18.04 LTS clang binary points to the 6.0 version:

  $ clang --version
  clang version 6.0.0-1ubuntu2 (tags/RELEASE_600/final)

However we can install clang-10 from the bionic-updates stream [*]
and use it, to silent the following warnings:

     CC      pc-bios/s390-ccw/main.o
  clang: warning: optimization flag '-fno-delete-null-pointer-checks' is not supported [-Wignored-optimization-argument]
  clang: warning: argument unused during compilation: '-msoft-float' [-Wunused-command-line-argument]
  /home/travis/build/qemu/qemu/pc-bios/s390-ccw/main.c:284:5: warning: no previous prototype for function 'main' [-Wmissing-prototypes]
  int main(void)
      ^
  1 warning generated.
  clang: warning: optimization flag '-fno-delete-null-pointer-checks' is not supported [-Wignored-optimization-argument]

[*] https://packages.ubuntu.com/bionic-updates/clang-10

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
---
However this doesn't resolve:

    /home/travis/build/philmd/qemu/pc-bios/s390-ccw/jump2ipl.c:67:18: error: invalid operand for instruction
        asm volatile("lghi 1,1\n\t"
                     ^
    <inline asm>:1:7: note: instantiated into assembly here
            lghi 1,1
                 ^
    /home/travis/build/philmd/qemu/pc-bios/s390-ccw/jump2ipl.c:67:29: error: invalid operand for instruction
        asm volatile("lghi 1,1\n\t"
                                ^
    <inline asm>:2:7: note: instantiated into assembly here
            diag 1,1,0x308
                 ^
    2 errors generated.
    Makefile:20: recipe for target 'jump2ipl.o' failed
    make[1]: *** [jump2ipl.o] Error 1

(see https://travis-ci.org/github/philmd/qemu/jobs/770920106#L1803,
https://travis-ci.org/github/philmd/qemu/jobs/770920522#L1818 for
more errors).
---
 .travis.yml | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/.travis.yml b/.travis.yml
index 4609240b5aa..9c0deea9a06 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -278,6 +278,7 @@ jobs:
       compiler: clang
       addons:
         apt_packages:
+          - clang-10
           - libaio-dev
           - libattr1-dev
           - libbrlapi-dev
@@ -303,7 +304,7 @@ jobs:
       env:
         - TEST_CMD="make check-unit"
         - CONFIG="--disable-containers --disable-tcg --enable-kvm
-                  --disable-tools --host-cc=clang --cxx=clang++"
+                  --disable-tools --host-cc=clang-10 --cc=clang-10 --cxx=clang++-10"
         - UNRELIABLE=true
 
     # Release builds
-- 
2.26.3