servo: Merge #19324 - Get back to working dir after vcvarsall.bat (from drewler:fix_matchbat); r=jdm

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When using cmd.exe directly (instead of `x86_x64 Cross Tools Command Prompt for VS 2017`), vcvarsall.bat changes the working directory.
To prevent this, pushd and popd could be used.

---
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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors

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- [X] These changes do not require tests because they are part of the build process.

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Source-Repo: https://github.com/servo/servo
Source-Revision: a20efc6d7bbbfa7261eea9a0aa534420724a1dbc

--HG--
extra : subtree_source : https%3A//hg.mozilla.org/projects/converted-servo-linear
extra : subtree_revision : 89a364953e569531902d36ce013b46ca19fca33b

servo/mach.bat

@@ -1,5 +1,7 @@
 @echo off
 
+pushd .
+
 IF EXIST "%ProgramFiles(x86)%" (
   set "ProgramFiles32=%ProgramFiles(x86)%"
 ) ELSE (
@@ -32,4 +34,6 @@ IF EXIST "%VS_VCVARS%" (
   EXIT /B
 )
 
+popd
+
 python mach %*