Explicit C99 support

We only use C99 for this program, so we should say so and test for it.

Signed-off-by: Joe Richey <joerichey@google.com>

.github/workflows/ci.yml

@@ -33,6 +33,8 @@ jobs:
       run: sudo apt-get install -y clang $TEST_DEPENDENCIES
     - name: Build and test
       run: make test-all CC=${{ matrix.compiler }}
+    - name: C99 check
+      run: make clean && make CC=${{ matrix.compiler }} CFLAGS="$CFLAGS -std=c99"
 
   build-and-test-32bit:
     name: Build and test (32-bit)

README.md

@@ -30,7 +30,7 @@ before using `fscryptctl`.
 ## Building and Installing
 
 To build `fscryptctl`, run `make`.  The only build dependencies are GNU Make and
-a C compiler.
+a C compiler (only C99 is needed).
 
 To install `fscryptctl`, run `sudo make install`.