./configure looks up most programs twice

There is a bug introduced in 6be2c5a7 where most tools are configured using AC_PATH_TOOL in the else clause of

if test "$HostOS" = "mingw32" -a "$EnableDistroToolchain" = "NO"; then

Result 1: Many of the later configure checks are skipped because by the time we get to them the relevant variables are set. (See #21778 (closed))

Result 2: AC_PATH_TOOL sets absolute paths rather than relative paths as AC_PROG_CC would set later on.

It seems the correct thing to do is to remove all these configure checks and replace it with something like:

--- a/configure.ac
+++ b/configure.ac
@@ -349,24 +349,8 @@ if test "$HostOS" = "mingw32" -a "$EnableDistroToolchain" = "NO"; then
     FP_INSTALL_WINDOWS_TOOLCHAIN
     FP_SETUP_WINDOWS_TOOLCHAIN([$hardtop/inplace/mingw], [$hardtop/inplace/mingw])
 else
-    AC_PATH_TOOL([CC],[gcc], [clang])
-    AC_PATH_TOOL([CXX],[g++], [clang++])
-    AC_PATH_TOOL([NM],[nm])
-    # N.B. we don't probe for LD here but instead
-    # do so in FIND_LD to avoid #21778.
-    AC_PATH_TOOL([AR],[ar])
-    AC_PATH_TOOL([RANLIB],[ranlib])
-    AC_PATH_TOOL([OBJDUMP],[objdump])
-    AC_PATH_TOOL([WindresCmd],[windres])
-    AC_PATH_TOOL([Genlib],[genlib])
-
-    if test "$HostOS" = "mingw32"; then
-        AC_CHECK_TARGET_TOOL([WindresCmd],[windres])
-        AC_CHECK_TARGET_TOOL([OBJDUMP],[objdump])
-
-        if test "$Genlib" != ""; then
-            GenlibCmd="$(cygpath -m $Genlib)"
-        fi
+    if "$TargetOS" = "mingw32"; then
+      AC_CHECK_TARGET_TOOL([WindresCmd],[windres])
     fi
 fi

Unfortunately fixing this issue is not immediately easy because ghc-toolchain is also setting absolute paths because findExecutable returns an absolute path.