Configure does not detect valgrind properly

[nagisa]

I do not yet have valgrind installed after a fresh Arch install and simple ./configure followed by make check-stage1 will either fail to compile jemalloc or

run rpass [x86_64-unknown-linux-gnu]: x86_64-unknown-linux-gnu/stage1/bin/compiletest
thread '<main>' panicked at 'Can't find Valgrind to run Valgrind tests', /home/nagisa/Documents/rust/rust/src/compiletest/compiletest.rs:50
/home/nagisa/Documents/rust/rust/mk/tests.mk:727: recipe for target 'tmp/check-stage1-T-x86_64-unknown-linux-gnu-H-x86_64-unknown-linux-gnu-rpass.ok' failed
make: *** [tmp/check-stage1-T-x86_64-unknown-linux-gnu-H-x86_64-unknown-linux-gnu-rpass.ok] Error 101

depending on your luck.

[brson]

Dupe of #18588