Merge bitcoin-core/secp256k1#1147: ci: print env to allow reproducing the job outside of CI

4e54c03153 ci: print env to allow reproducing the job outside of CI (Jonas Nick)

Pull request description:

  Example output:

  ```
  WERROR_CFLAGS="-Werror -pedantic-errors"  MAKEFLAGS="-j4"  BUILD="check"  ECMULTWINDOW="auto"  ECMULTGENPRECISION="auto"  ASM="no"  WIDEMUL="int64"  WITH_VALGRIND="no"  EXTRAFLAGS=""  EXPERIMENTAL="no"  ECDH="no"  RECOVERY="yes"  SCHNORRSIG="no"  SECP256K1_TEST_ITERS=""  BENCH="yes"  SECP256K1_BENCH_ITERS="2"  CTIMETEST="yes"  EXAMPLES="yes"  WRAPPER_CMD=""  CC="gcc"  AR=""  NM=""  HOST=""  ./ci/cirrus.sh
  ```

ACKs for top commit:
  sipa:
    ACK 4e54c03153
  real-or-random:
    ACK 4e54c03153

Tree-SHA512: b74a8724e72b3de7884e4d93fe933dc5043aec37020672b7997a8faebda3b0cbbba1bca69c344109729261ab4a94e76f4eca0d8773dc101a443fdf9e0d7d54f5

ci/cirrus.sh

@@ -5,6 +5,26 @@ set -x
 
 export LC_ALL=C
 
+# Print relevant CI environment to allow reproducing the job outside of CI.
+print_environment() {
+    # Turn off -x because it messes up the output
+    set +x
+    # There are many ways to print variable names and their content. This one
+    # does not rely on bash.
+    for i in WERROR_CFLAGS MAKEFLAGS BUILD \
+            ECMULTWINDOW ECMULTGENPRECISION ASM WIDEMUL WITH_VALGRIND EXTRAFLAGS \
+            EXPERIMENTAL ECDH RECOVERY SCHNORRSIG \
+            SECP256K1_TEST_ITERS BENCH SECP256K1_BENCH_ITERS CTIMETEST\
+            EXAMPLES \
+            WRAPPER_CMD CC AR NM HOST
+    do
+        eval 'printf "%s %s " "$i=\"${'"$i"'}\""'
+    done
+    echo "$0"
+    set -x
+}
+print_environment
+
 # Start persistent wineserver if necessary.
 # This speeds up jobs with many invocations of wine (e.g., ./configure with MSVC) tremendously.
 case "$WRAPPER_CMD" in