ci: add gcc to fix build

Zig relies on the existence of a system c compiler in order to
find the native libc include paths.

 .github/workflows/ci_build.yml | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/.github/workflows/ci_build.yml b/.github/workflows/ci_build.yml
index 65c3077..58dee0b 100644
--- a/.github/workflows/ci_build.yml
+++ b/.github/workflows/ci_build.yml
@@ -23,7 +23,7 @@ jobs:
           xbps-install -S
           xbps-install -uy xbps
           xbps-install -uy zig wayland-devel wayland-protocols wlroots-devel \
-          	libxkbcommon-devel pixman-devel pkgconf scdoc git
+            libxkbcommon-devel pixman-devel pkgconf scdoc git gcc
 
       - name: checkout
         uses: actions/checkout@v2
@@ -50,7 +50,7 @@ jobs:
           xbps-install -uy xbps
           xbps-install -uy
           xbps-install -uy zig wayland-devel wayland-protocols wlroots-devel \
-          	libxkbcommon-devel pixman-devel pkgconf scdoc git
+            libxkbcommon-devel pixman-devel pkgconf scdoc git gcc
 
       - name: checkout
         uses: actions/checkout@v2