Tweak Makefile logic for tesseract/leptonica.

Firstly, we don't set HAVE_LEPTONICA or HAVE_TESSERACT if they
have already been set.

Secondly, correct the ifeq() logic to use brackets around $(HAVE_...)
to keep xcode (at least) happy.

Makerules

@@ -147,14 +147,14 @@ else ifeq ($(OS),Linux)
 	SYS_ZLIB_LIBS := $(shell pkg-config --libs zlib)
   endif
 
-  HAVE_LEPTONICA := $(shell pkg-config --exists 'lept >= 1.7.4' && echo yes)
-  ifeq ($(HAVE_LEPTONICA),yes)
+  HAVE_SYS_LEPTONICA := $(shell pkg-config --exists 'lept >= 1.7.4' && echo yes)
+  ifeq ($(HAVE_SYS_LEPTONICA),yes)
 	SYS_LEPTONICA_CFLAGS := $(shell pkg-config --cflags lept)
 	SYS_LEPTONICA_LIBS := $(shell pkg-config --libs lept)
   endif
 
-  HAVE_TESSERACT := $(shell pkg-config --exists 'tesseract-ocr >= 4.0.0' && echo yes)
-  ifeq ($(HAVE_TESSERACT),yes)
+  HAVE_SYS_TESSERACT := $(shell pkg-config --exists 'tesseract >= 4.0.0' && echo yes)
+  ifeq ($(HAVE_SYS_TESSERACT),yes)
 	SYS_TESSERACT_CFLAGS := $(shell pkg-config --cflags tesseract)
 	SYS_TESSERACT_LIBS := $(shell pkg-config --libs tesseract)
   endif

Makethird

@@ -25,19 +25,24 @@ ifeq ($(OS),Linux)
   USE_SYSTEM_CURL := yes
 endif
 
-ifneq ($(USE_SYSTEM_LEPTONICA),yes)
-ifeq ($(wildcard thirdparty/leptonica/src/*),)
-  HAVE_LEPTONICA := no
+ifeq ($(USE_SYSTEM_LEPTONICA),yes)
+  HAVE_LEPTONICA := $(HAVE_SYS_LEPTONICA)
 else
-  HAVE_LEPTONICA := yes
-endif
+  ifeq ($(wildcard thirdparty/leptonica/src/*),)
+    HAVE_LEPTONICA := no
+  else
+    HAVE_LEPTONICA := yes
+  endif
 endif
-ifneq ($(USE_SYSTEM_TESSERACT),yes)
-ifeq ($(wildcard thirdparty/tesseract/src/*),)
-  HAVE_TESSERACT := no
+
+ifeq ($(USE_SYSTEM_TESSERACT),yes)
+  HAVE_TESSERACT := $(HAVE_SYS_TESSERACT)
 else
-  HAVE_TESSERACT := yes
-endif
+  ifeq ($(wildcard thirdparty/tesseract/src/*),)
+    HAVE_TESSERACT := no
+  else
+    HAVE_TESSERACT := yes
+  endif
 endif
 
 ifeq ($(HAVE_LEPTONICA),yes)
@@ -809,24 +814,24 @@ THIRD_SRC += thirdparty/tesseract/src/wordrec/wordrec.cpp
 
 THIRD_CFLAGS += -Ithirdparty/tesseract/include -Iscripts/tesseract
 
-ifeq ($HAVE_AVX,yes)
+ifeq ($(HAVE_AVX),yes)
 TESSERACT_AVX_FLAGS = -mavx -DHAVE_AVX -D__AVX__
 THIRD_SRC += thirdparty/tesseract/src/arch/dotproductavx.cpp
 endif
-ifeq ($HAVE_AVX2,yes)
+ifeq ($(HAVE_AVX2),yes)
 TESSERACT_AVX2_FLAGS = -mavx2 -DHAVE_AVX2 -D__AVX2__
 THIRD_SRC += thirdparty/tesseract/src/arch/intsimdmatrixavx2.cpp
 endif
-ifeq ($HAVE_FMA,yes)
+ifeq ($(HAVE_FMA),yes)
 TESSERACT_FMA_FLAGS = -mfma -DHAVE_FMA -D__FMA__
 THIRD_SRC += thirdparty/tesseract/src/arch/dotproductfma.cpp
 endif
-ifeq ($HAVE_SSE4_1,yes)
+ifeq ($(HAVE_SSE4_1),yes)
 TESSERACT_SSE_FLAGS = -msse4.1 -DHAVE_SSE4_1 -D__SSE4_1__
 THIRD_SRC += thirdparty/tesseract/src/arch/dotproductsse.cpp
 THIRD_SRC += thirdparty/tesseract/src/arch/intsimdmatrixsse.cpp
 endif
-ifeq ($HAVE_NEON,yes)
+ifeq ($(HAVE_NEON),yes)
 TESSERACT_NEON_FLAGS = -mneon -DHAVE_NEON
 THIRD_SRC += thirdparty/tesseract/src/arch/intsimdmatrixneon.cpp
 endif