Leaner TIS-CI tests

TIS-CI tests take forever.  It's annoying and cost them compute power
for little benefit.  A quick assesment of Monocypher reveals that the
only things we really care about are endianness and main word size.
Things like the sign of `char`, `sizeof(int)`, or `long double` are
mostly (or entirely) irrelevant.

So, all platforms supported by TIS-CI, only 5 are relevant:

- 16-bits little endian (I chose x86_16)
- 32-bits little endian (I chose x86_32)
- 32-bits big    endian (I chose sparc_32)
- 32-bits little endian (I chose rv64ifdq)
- 32-bits big    endian (I chose mips_64)

All the others are redundant.

---

Also added the missing v_x25519 test.

tests/tis-ci-gen-config.sh

@@ -70,6 +70,7 @@ for entry_point in      \
     "v_sha512_hmac"     \
     "v_sha512_hkdf"     \
     "v_argon2"          \
+    "v_x25519"          \
     "v_edDSA"           \
     "v_edDSA_pk"        \
     "v_ed_25519"        \
@@ -84,16 +85,11 @@ for entry_point in      \
     "p_verify64"
 do
     for platform in   \
+        "x86_16"      \
         "sparc_32"    \
         "x86_32"      \
-        "x86_16"      \
-        "x86_win64"   \
-        "armeb_eabi"  \
-        "arm_eabi"    \
-        "aarch64"     \
         "rv64ifdq"    \
-        "mips_64"     \
-        "ppc_64"
+        "mips_64"
     do
         echo '{ "name"          :' "\"$entry_point - $platform\"" >> $TIS_CONFIG
         echo ', "files"         :'                                >> $TIS_CONFIG