Re: [libvirt PATCH] build: workaround behaviour regression in gnu make 4.3

We need the "$(space)" variable to contain a single whitespace character. We do this by assigning and then appending an empty string to the variable. Variable appends get separated by a single whitespace historically, but GNU make 4.3 introduced a behaviour regression. https://lists.gnu.org/archive/html/bug-make/2020-01/msg00057.html [quote] * WARNING: Backward-incompatibility! Previously appending using '+=' to an empty variable would result in a value starting with a space. Now the initial space is only added if the variable already contains some value. Similarly, appending an empty string does not add a trailing space. [/quote] This patch tries a new trick to get a single whitespace by getting make to expand two non-existant variables separated by a space.