remote attach: use absolute /bin/sh path on Linux

When using machinectl as a transport to connect the debugger to
a nspawn container, we need to pass full paths when running commands,
as that's what machinectl expects. Use /bin/sh when running on Linux.
This allows connecting VSCode to nspawn containers.

https://www.freedesktop.org/software/systemd/man/machinectl.html
https://www.freedesktop.org/software/systemd/man/systemd-nspawn.html

Extension/src/Debugger/attachToProcess.ts

@@ -112,6 +112,7 @@ export class RemoteAttachPicker {
         let parameterBegin: string = `$(`;
         let parameterEnd: string = `)`;
         let escapedQuote: string = `\\\"`;
+        let shPrefix: string = ``;
 
         const settings: CppSettings = new CppSettings();
         if (settings.useBacktickCommandSubstitution) {
@@ -122,12 +123,14 @@ export class RemoteAttachPicker {
 
         // Must use single quotes around the whole command and double quotes for the argument to `sh -c` because Linux evaluates $() inside of double quotes.
         // Having double quotes for the outerQuote will have $(uname) replaced before it is sent to the remote machine.
+        // Also use a full path on Linux, so that we can use transports that need a full patch such as 'machinectl' to connect to nspawn containers.
         if (os.platform() !== "win32") {
             innerQuote = `"`;
             outerQuote = `'`;
+            shPrefix = `/bin/`;
         }
 
-        return `${outerQuote}sh -c ${innerQuote}uname && if [ ${parameterBegin}uname${parameterEnd} = ${escapedQuote}Linux${escapedQuote} ] ; ` +
+        return `${outerQuote}${shPrefix}sh -c ${innerQuote}uname && if [ ${parameterBegin}uname${parameterEnd} = ${escapedQuote}Linux${escapedQuote} ] ; ` +
             `then ${PsProcessParser.psLinuxCommand} ; elif [ ${parameterBegin}uname${parameterEnd} = ${escapedQuote}Darwin${escapedQuote} ] ; ` +
             `then ${PsProcessParser.psDarwinCommand}; fi${innerQuote}${outerQuote}`;
     }