I've gotten this a couple times, so I'm reporting it now. I've gotten it a couple of times trying to build xmlada in particular inside Windows terminal. My current workaround is to re-run the same alr build command from an msys64 window instead.

Once the build has succeeded initially I have no further problems.

PS D:\dev\ada\septum\tests> alr build
Note: Synchronizing workspace...
Dependencies automatically updated as follows:

   +  ansiada             0.1.0    (new,indirect)
   +  dir_iterators       0.0.3    (new,indirect)
   +i gnat                10.3.0-1 (new,installed,gnat_native,indirect)
   +  gnatcoll            21.0.0   (new,indirect)
   +  libgpr              21.0.0   (new,indirect)
   +  progress_indicators 0.0.1    (new,indirect)
   +┬╖ septum              0.0.1    (new,path=../../septum)
   +  trendy_test         0.0.1    (new)
   +  xmlada              21.0.0   (new,indirect)
Note: Deploying release ansiada=0.1.0...
Cloning into 'D:\dev\ada\septum\tests\alire\cache\dependencies\alr-xual.tmp'...
remote: Enumerating objects: 50, done.
remote: Counting objects: 100% (50/50), done.
remote: Compressing objects: 100% (34/34), done.
remote: Total 50 (delta 16), reused 38 (delta 11), pack-reused 0
Receiving objects: 100% (50/50), 10.74 KiB | 5.37 MiB/s, done.
Resolving deltas: 100% (16/16), done.
Note: Deploying release dir_iterators=0.0.3...
Cloning into 'D:\dev\ada\septum\tests\alire\cache\dependencies\alr-insz.tmp'...
remote: Enumerating objects: 89, done.
remote: Counting objects: 100% (89/89), done.
remote: Compressing objects: 100% (55/55), done.
Receiving objects:  79% (71/89)
Receiving objects: 100% (89/89), 20.21 KiB | 10.10 MiB/s, done.
Resolving deltas: 100% (46/46), done.
Note: Deploying release trendy_test=0.0.1...
Cloning into 'D:\dev\ada\septum\tests\alire\cache\dependencies\alr-kyql.tmp'...
remote: Enumerating objects: 185, done.
remote: Counting objects: 100% (185/185), done.
remote: Compressing objects: 100% (113/113), done.
remote: Total 185 (delta 121), reused 123 (delta 67), pack-reused 0
Receiving objects: 100% (185/185), 35.49 KiB | 908.00 KiB/s, done.
Resolving deltas: 100% (121/121), done.
Note: Deploying release xmlada=21.0.0...
############################################################################################################################# 100.0%## # -=O=-
Cannot find required tool: UNZIP
Do you want Alire to install the required tool?
[Y] Yes  [N] No  (default is Yes) yes
resolving dependencies...
looking for conflicting packages...

Packages (1) unzip-6.0-2

Total Download Size:   0.09 MiB
Total Installed Size:  0.45 MiB

:: Proceed with installation? [Y/n]
:: Retrieving packages...
 unzip-6.0-2-x86_64                                  93.1 KiB  73.5 KiB/s 00:01 [############################################] 100%
(1/1) checking keys in keyring                                                  [############################################] 100%
(1/1) checking package integrity                                                [############################################] 100%
(1/1) loading package files                                                     [############################################] 100%
(1/1) checking for file conflicts                                               [############################################] 100%
(1/1) checking available disk space                                             [############################################] 100%
:: Processing package changes...
(1/1) installing unzip                                                          [############################################] 100%
Note: Running post_fetch actions for xmlada=21.0.0...
configure: loading site script /usr/local/etc/config.site
checking build system type... ./config.guess: unable to guess system type

This script, last modified 2013-06-10, has failed to recognize
the operating system you are using. It is advised that you
download the most up to date version of the config scripts from

  http://git.savannah.gnu.org/gitweb/?p=config.git;a=blob_plain;f=config.guess;hb=HEAD
and
  http://git.savannah.gnu.org/gitweb/?p=config.git;a=blob_plain;f=config.sub;hb=HEAD

If the version you run (./config.guess) is already up to date, please
send the following data and any information you think might be
pertinent to <[email protected]> in order to provide the needed
information to handle your system.

config.guess timestamp = 2013-06-10

uname -m = x86_64
uname -r = 3.2.0-340.x86_64
uname -s = MSYS_NT-10.0-19041
uname -v = 2021-08-02 16:30 UTC

/usr/bin/uname -p = unknown
/bin/uname -X     =

hostinfo               =
/bin/universe          =
/usr/bin/arch -k       =
/bin/arch              = x86_64
/usr/bin/oslevel       =
/usr/convex/getsysinfo =

UNAME_MACHINE = x86_64
UNAME_RELEASE = 3.2.0-340.x86_64
UNAME_SYSTEM  = MSYS_NT-10.0-19041
UNAME_VERSION = 2021-08-02 16:30 UTC
configure: error: cannot guess build type; you must specify one
ERROR: Command ["sh", "configure"] exited with code 1