Allow custom definition of GIT.

(cherry picked from commit f6636c9c1c447ce1a2018b3389257c7bc0870a74)

compiler/Makefile

@@ -404,7 +404,9 @@ ifndef RTLOPT
 RTLOPT:=$(OPT)
 endif
 SVNVERSION:=$(firstword $(wildcard $(addsuffix /svnversion$(SRCEXEEXT),$(SEARCHPATH))))
+ifndef GIT
 GIT:=$(firstword $(wildcard $(addsuffix /git$(SRCEXEEXT),$(SEARCHPATH))))
+endif
 DATE_FMT = +%Y/%m/%d
 ifdef SOURCE_DATE_EPOCH
     COMPDATESTR ?= $(shell date -u -d "@$(SOURCE_DATE_EPOCH)" "$(DATE_FMT)" 2>/dev/null || date -u -r "$(SOURCE_DATE_EPOCH)" "$(DATE_FMT)" 2>/dev/null || date -u "$(DATE_FMT)")

compiler/Makefile.fpc

@@ -130,7 +130,10 @@ RTLOPT:=$(OPT)
 endif
 
 SVNVERSION:=$(firstword $(wildcard $(addsuffix /svnversion$(SRCEXEEXT),$(SEARCHPATH))))
+
+ifndef GIT
 GIT:=$(firstword $(wildcard $(addsuffix /git$(SRCEXEEXT),$(SEARCHPATH))))
+endif
 
 DATE_FMT = +%Y/%m/%d
 ifdef SOURCE_DATE_EPOCH