Fix usage of CFLAGS with cmake in all.sh

With cmake, CFLAGS has to be set when invoking cmake, not make (which totally
ignores the value of CFLAGS when it runs and only keeps the one from cmake).

Also, in that case the flags were either redundant (-Werror etc) or wrong
(-std=c99 -pedantic) as some parts of the library will not build with
-pedantic (see the other -pedantic tests, which are correct, for what needs to
be disabled).
diff --git a/tests/scripts/all.sh b/tests/scripts/all.sh
index 1a891fd..cae1c72 100755
--- a/tests/scripts/all.sh
+++ b/tests/scripts/all.sh
@@ -530,16 +530,16 @@
 msg "test: !MBEDTLS_SSL_RENEGOTIATION - ssl-opt.sh (ASan build)" # ~ 6 min
 if_build_succeeded tests/ssl-opt.sh
 
-msg "build: cmake, full config, clang, C99" # ~ 50s
+msg "build: cmake, full config, clang" # ~ 50s
 cleanup
 cp "$CONFIG_H" "$CONFIG_BAK"
 scripts/config.pl full
 scripts/config.pl unset MBEDTLS_MEMORY_BACKTRACE # too slow for tests
 CC=clang cmake -D CMAKE_BUILD_TYPE:String=Check -D ENABLE_TESTING=On .
-make CFLAGS='-Werror -Wall -Wextra -std=c99 -pedantic'
+make
 
 msg "test: main suites (full config)" # ~ 5s
-make CFLAGS='-Werror -Wall -Wextra' test
+make test
 
 msg "test: ssl-opt.sh default (full config)" # ~ 1s
 if_build_succeeded tests/ssl-opt.sh -f Default