Failure installing rvm on Windows 10 using cygwin64... __rvm_make -j8 - windows

Question

Trying to install rvm on Windows 10 using cygwin64.
Have updated path to include cygwin64\bin to get past some other issues.
Now it's failing after significant progress...
$ rvm install "ruby-2.5.3"
ruby-2.5.3 - #removing src/ruby-2.5.3..
Searching for binary rubies, this might take some time.
No binary rubies available for: cygwin/unknown/x86_64/ruby-2.5.3.
Continuing with compilation. Please read 'rvm help mount' to get more information on binary rubies.
Checking requirements for cygwin.
Requirements installation successful.
Installing Ruby from source to: /home/wmbra/.rvm/rubies/ruby-2.5.3, this may take a while depending on your cpu(s)...
ruby-2.5.3 - #downloading ruby-2.5.3, this may take a while depending on your connection...
ruby-2.5.3 - #extracting ruby-2.5.3 to /home/wmbra/.rvm/src/ruby-2.5.3.....
ruby-2.5.3 - #configuring...................................................................
ruby-2.5.3 - #post-configuration..
ruby-2.5.3 - #compiling..............................................................
**Error running '__rvm_make -j8',
please read /home/wmbra/.rvm/log/1674057369_ruby-2.5.3/make.log
**
There has been an error while running make. Halting the installation.
Looking at the last lines of make.log below, it appears that gcc is not found in bin/sh
...
compiling cygruby250.res.o
make[1]: Entering directory '/home/wmbra/.rvm/src/ruby-2.5.3'
make[1]: Nothing to be done for 'srcs'.
make[1]: Leaving directory '/home/wmbra/.rvm/src/ruby-2.5.3'
**generating transdb.h
/bin/sh: gcc -E -xc: command not found
windres: preprocessing failed.
**make: *** [GNUmakefile:48: cygruby250.res.o] Error 1
make: *** Waiting for unfinished jobs....
transdb.h updated
rm cygruby250.rc
++ return 2
gcc.exe is sitting in cygwin64/bin. Not sure what the /sh reference is.
Any help understanding / resolving would be very much appreciated!
**Tried:
**
$ rvm install "ruby-2.5.3"
**Expected:
**successful install of rvm :)
**Actual:
**
**Error running '__rvm_make -j8',
please read /home/wmbra/.rvm/log/1674057369_ruby-2.5.3/make.log