[PATCH v2] travis.yml: Add missing 'flex', 'bison' packages to 'GCC (user)' job

[Vaibhav Jain <vaibhav@linux.ibm.com>]

Since commit fd8171fe52b5e("target/hexagon: import lexer for idef-parser") the
hexagon target uses 'flex', 'bison' to generate idef-parser. However default
travis builder image for 'focal' may not have these pre-installed, consequently
following error is seen with travis when trying to execute the 'GCC (user)' job
that also tries to build hexagon user binary:

<snip>
export CONFIG="--disable-containers --disable-system"
<snip>
 Program flex found: NO

../target/hexagon/meson.build:179:4: ERROR: Program 'flex' not found or not
executable
<snip>

Fix this by explicitly add 'flex' and 'bison' to the list of addon apt-packages
for the 'GCC (user)' job.

Signed-off-by: Vaibhav Jain <vaibhav@linux.ibm.com>
---
Changelog:

Since v1:
Link: https://lore.kernel.org/qemu-devel/20230414210645.820204-2-vaibhav@linux.ibm.com/

- Added 'bison' also to the addon package list (Thomas)
- Updated the patch description
---
 .travis.yml | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/.travis.yml b/.travis.yml
index 11894eb810..b958eca5de 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -237,6 +237,8 @@ jobs:
           - libglib2.0-dev
           - libgnutls28-dev
           - ninja-build
+          - flex
+          - bison
       env:
         - CONFIG="--disable-containers --disable-system"
 
-- 
2.39.2