ghc-7.4.2 fails to build on osx-12.1.0

[easye]

Building ghc-7.4.2 fails to build complaining about not being able to execute /opt/local/bin/gcc-mp-4.7:

"inplace/bin/ghc-stage1" -prof  -H32m -O    -package-name ghc-7.4.2 -hide-all-packages -i -icompiler/basicTypes -icompiler/cmm -icompiler/codeGen -icompiler/coreSyn -icompiler/deSugar -icompiler/ghci -icompiler/hsSyn -icompiler/iface -icompiler/llvmGen -icompiler/main -icompiler/nativeGen -icompiler/parser -icompiler/prelude -icompiler/profiling -icompiler/rename -icompiler/simplCore -icompiler/simplStg -icompiler/specialise -icompiler/stgSyn -icompiler/stranal -icompiler/typecheck -icompiler/types -icompiler/utils -icompiler/vectorise -icompiler/stage2/build -icompiler/stage2/build/autogen -Icompiler/stage2/build -Icompiler/stage2/build/autogen -Icompiler/../rts/dist/build -Icompiler/stage2 -Icompiler/../libraries/base/cbits -Icompiler/../libraries/base/include -Icompiler/. -Icompiler/parser -Icompiler/utils   -optP-DGHCI -optP-include -optPcompiler/stage2/build/autogen/cabal_macros.h -package Cabal-1.14.0 -package array-0.4.0.0 -package base-4.5.1.0 -package bin-package-db-0.0.0.0 -package bytestring-0.9.2.1 -package containers-0.4.2.1 -package directory-1.1.0.2 -package filepath-1.3.0.0 -package hoopl-3.8.7.3 -package hpc-0.5.1.1 -package old-time-1.1.0.0 -package process-1.1.0.1 -package template-haskell-2.7.0.0 -package unix-2.5.1.1  -Wall -fno-warn-name-shadowing -fno-warn-orphans -XHaskell98 -XNondecreasingIndentation -XCPP -XMagicHash -XUnboxedTuples -XPatternGuards -XForeignFunctionInterface -XEmptyDataDecls -XTypeSynonymInstances -XMultiParamTypeClasses -XFlexibleInstances -XRank2Types -XScopedTypeVariables -XDeriveDataTypeable -XBangPatterns -DGHCI_TABLES_NEXT_TO_CODE -DSTAGE=2 -O2  -no-user-package-conf -rtsopts     -odir compiler/stage2/build -hidir compiler/stage2/build -stubdir compiler/stage2/build -hisuf p_hi -osuf  p_o -hcsuf p_hc -c compiler/parser/LexCore.hs -o compiler/stage2/build/LexCore.p_o
ghc-stage1: could not execute: /opt/local/bin/gcc-mp-4.7
make[1]: *** [libraries/template-haskell/dist-install/build/Language/Haskell/TH/Syntax.o] Error 1
make[1]: *** Waiting for unfinished jobs....
make: *** [all] Error 2
make: Leaving directory `/opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_release_tarballs_ports_lang_ghc/ghc/work/ghc-7.4.2'
Command failed:  cd "/opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_release_tarballs_ports_lang_ghc/ghc/work/ghc-7.4.2" && /usr/bin/make -j4 -w all 
Exit code: 2
Error: org.macports.build for port ghc returned: command execution failed
Warning: targets not executed for ghc: org.macports.activate org.macports.build org.macports.destroot org.macports.install
Error: Failed to install ghc

which is an odd message as the "inplace/bin/ghc-stage1" script gets used succesfully previously in the build, and

tethys:~$ ls -l /opt/local/bin/gcc-mp-4.7 
-rwxr-xr-x  3 root  admin  778760 Sep 12 12:46 /opt/local/bin/gcc-mp-4.7*
tethys:~$ /opt/local/bin/gcc-mp-4.7 --version
gcc-mp-4.7 (MacPorts gcc47 4.7.1_4) 4.7.1
Copyright (C) 2012 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

[neverpanic (Clemens Lang)]

I've seen similar issues which magically vanished when re-attempting the build. Can you just re-try and see if the issue persists? Also consider disabling parallel builds by appending build.jobs=1 to the command line you use to install ghc.

[neverpanic (Clemens Lang)]

I assume this was due to parallel build being enabled; disabled them in r97866.