roachtest: do not build arm64 and fips variants when their probabilities are 0

Previously, even when the probabilities for arm64 and fips builds were set to 0,
the nightly roachtest script would still build those variants, which is unnecessary
and wasteful. This change modifies the script to skip building arm64 and fips
variants when their respective probabilities are set to 0.

Epic: none
Release note: none

Author: rail

build/teamcity/cockroach/nightlies/roachtest_nightly_impl.sh

@@ -19,15 +19,26 @@ if [[ ! -f ~/.ssh/id_rsa.pub ]]; then
   ssh-keygen -q -C "roachtest-nightly-bazel $(date)" -N "" -f ~/.ssh/id_rsa
 fi
 
+arm_probability="${ARM_PROBABILITY:-0.5}"
+fips_probability="${FIPS_PROBABILITY:-0.02}"
+
 arch=amd64
 if [[ ${CLOUD} == "ibm" ]]; then
   arch=s390x
 fi
 $root/build/teamcity/cockroach/nightlies/roachtest_compile_bits.sh $arch
 if [[ $arch != "s390x" ]]; then
-  $root/build/teamcity/cockroach/nightlies/roachtest_compile_bits.sh arm64
+  # Do not build arm64 if the probability is 0.
+  # Use `bc` for float comparison, bash supports only integer comparison.
+  if (( $(echo "$arm_probability > 0" | bc -l) )); then
+    $root/build/teamcity/cockroach/nightlies/roachtest_compile_bits.sh arm64
+  fi
   # N.B. FIPS is metamoprhically always on as of PR#139510
-  $root/build/teamcity/cockroach/nightlies/roachtest_compile_bits.sh amd64-fips
+  # Do not build fips if the probability is 0.
+  # Use `bc` for float comparison, bash supports only integer comparison.
+  if (( $(echo "$fips_probability > 0" | bc -l) )); then
+    $root/build/teamcity/cockroach/nightlies/roachtest_compile_bits.sh amd64-fips
+  fi
 fi
 
 artifacts=/artifacts
@@ -89,8 +100,8 @@ fi
 #
 build/teamcity-roachtest-invoke.sh \
   --metamorphic-encryption-probability=0.5 \
-  --metamorphic-arm64-probability="${ARM_PROBABILITY:-0.5}" \
-  --metamorphic-fips-probability="${FIPS_PROBABILITY:-0.02}" \
+  --metamorphic-arm64-probability="$arm_probability" \
+  --metamorphic-fips-probability="$fips_probability" \
   --metamorphic-cockroach-ea-probability="${COCKROACH_EA_PROBABILITY:-0.2}" \
   ${select_probability:-} \
   --always-collect-artifacts="${ALWAYS_COLLECT_ARTIFACTS:-false}" \