Just to jump in with an issue I had compiling the SDK. I'm using the new bash shell under Windows 10.
[CFG ] checking that generated files are newer than configure... done
[CFG ] configure: creating ./config.status
[CFG ] config.status: creating Makefile
[CFG ] config.status: creating doc/Makefile
[CFG ] config.status: creating src/Makefile
[CFG ] config.status: creating tests/Makefile
[CFG ] config.status: creating tune/Makefile
[CFG ] config.status: creating src/mparam.h
[CFG ] config.status: executing depfiles commands
[CFG ] config.status: executing libtool commands
[EXTRA] Building MPFR
[DEBUG] ==> Executing: '/usr/bin/make' '-j5' '-l'
[ALL ] make[3]: Entering directory `/mnt/c/Users/Pete/Documents/esp8266/build/esp-open-sdk/crosstool-NG/.build/xtens
a-lx106-elf/build/build-mpfr-host-x86_64-build_pc-linux-gnu'
[ALL ] CDPATH="${ZSH_VERSION+.}:" && cd /mnt/c/Users/Pete/Documents/esp8266/build/esp-open-sdk/crosstool-NG/.build/s
rc/mpfr-3.1.3 && /bin/bash /mnt/c/Users/Pete/Documents/esp8266/build/esp-open-sdk/crosstool-NG/.build/src/mpfr-3.1.3/mis
sing aclocal-1.15 -I m4
[ALL ] /mnt/c/Users/Pete/Documents/esp8266/build/esp-open-sdk/crosstool-NG/.build/src/mpfr-3.1.3/missing: line 81: a
clocal-1.15: command not found
[ALL ] WARNING: 'aclocal-1.15' is missing on your system.
[ALL ] You should only need it if you modified 'acinclude.m4' or
[ALL ] 'configure.ac' or m4 files included by 'configure.ac'.
[ALL ] The 'aclocal' program is part of the GNU Automake package:
[ALL ] <
http://www.gnu.org/software/automake>
[ALL ] It also requires GNU Autoconf, GNU m4 and Perl in order to run:
[ALL ] <
http://www.gnu.org/software/autoconf>
[ALL ] <
http://www.gnu.org/software/m4/>
[ALL ] <
http://www.perl.org/>
[ERROR] make[3]: *** [/mnt/c/Users/Pete/Documents/esp8266/build/esp-open-sdk/crosstool-NG/.build/src/mpfr-3.1.3/acloc
al.m4] Error 127
[ALL ] make[3]: Leaving directory `/mnt/c/Users/Pete/Documents/esp8266/build/esp-open-sdk/crosstool-NG/.build/xtensa
-lx106-elf/build/build-mpfr-host-x86_64-build_pc-linux-gnu'
[ERROR]
[ERROR] >>
[ERROR] >> Build failed in step 'Installing MPFR for host'
[ERROR] >> called in step '(top-level)'
[ERROR] >>
[ERROR] >> Error happened in: CT_DoExecLog[scripts/functions@257]
[ERROR] >> called from: do_mpfr_backend[scripts/build/companion_libs/110-mpfr.sh@149]
[ERROR] >> called from: do_mpfr_for_host[scripts/build/companion_libs/110-mpfr.sh@104]
[ERROR] >> called from: do_companion_libs_for_host[scripts/build/companion_libs.sh@36]
[ERROR] >> called from: main[scripts/crosstool-NG.sh@646]
[ERROR] >>
[ERROR] >> For more info on this error, look at the file: 'build.log'
[ERROR] >> There is a list of known issues, some with workarounds, in:
[ERROR] >> 'share/doc/crosstool-ng/crosstool-ng-1.22.0-55-gecfc19a/B - Known issues.txt'
[ERROR]
[ERROR] (elapsed: 16:04.29)
A google search suggests that the issue has to do with timestamp on the file configure.ac being newer than aclocal.m4 making make think that something needs to be rebuilt, but I'm not sure how to resolve this.