.travis.yml: change -std=c89 to -ansi

For C, -ansi is equivalent to -std=c90
For C++, -ansi is equivalent to -std=c++98

We also place -ansi in CPPFLAGS instead of the usual command line config,
to avoid getting it when linking (clang complains)

(cherry picked from commit 874f785988c17991051d36a0407a87b36c463a94)
Reviewed-by: NPaul Dale <paul.dale@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/8359)

.travis.yml

@@ -28,7 +28,7 @@ compiler:
 env:
     - CONFIG_OPTS="" DESTDIR="_install"
     - CONFIG_OPTS="no-asm -Werror --debug no-afalgeng no-shared enable-crypto-mdebug enable-rc5 enable-md2"
-    - CONFIG_OPTS="no-asm no-makedepend --strict-warnings -std=c89 -D_DEFAULT_SOURCE" BUILDONLY="yes" CHECKDOCS="yes" GENERATE="yes"
+    - CONFIG_OPTS="no-asm no-makedepend --strict-warnings -D_DEFAULT_SOURCE" BUILDONLY="yes" CHECKDOCS="yes" GENERATE="yes" CPPFLAGS="-ansi"
 
 matrix:
     include: