I did this

I am currently building curl-7.55.1 for Windows 64bit.
This issue may have been detected but could not find any mention of it.

mt.exe : general error c10100b1: Failed to load file "..\builds\libcurl-vc9-x64-debug-dll\curl.exe". The system cannot find the file specified.
NMAKE : fatal error U1077: '"C:\Program Files\Microsoft SDKs\Windows\v6.0A\bin\mt.EXE"' : return code '0x1f' Stop.
NMAKE : fatal error U1077: '"c:\Program Files (x86)\Microsoft Visual Studio 9.0\VC\BIN\nmake.exe"' : return code '0x2'

In MakefileBuild.vc:

!IFDEF EMBED_MANIFEST
MANIFESTTOOL = mt -manifest $(DIRDIST)\$(PROGRAM_NAME).manifest -outputresource:$(DIRDIST)\$(PROGRAM_NAME);1
!ENDIF

Needs to be changed: \bin is missing from the 2 paths.

MANIFESTTOOL = mt -manifest $(DIRDIST)\bin\$(PROGRAM_NAME).manifest -outputresource:$(DIRDIST)\bin\$(PROGRAM_NAME);1